Optical film, polarizing plate and display device utilizing the film, and production method of optical film

ABSTRACT

An optical film obtained by a process comprising the steps of:  
     (a) casting a dope comprising a cellulose ester and a non-chlorinated solvent on a metal support, the cellulose ester having a total acyl substitution degree of 2.6 to 2.85 and having a ratio of a weight-average molecular weight to a number-average molecular weight of 1:1 to 3:1;  
     (b) drying the cast dope on the metal support so as to obtain a cellulose ester film;  
     (c) pealing the cellulose ester film from the metal support;  
     (d) further drying the cellulose ester film while providing a longitudinal stretch or a lateral stretch to the cellulose ester film; and  
     (e) providing a metal oxide layer on the cellulose ester film.

FIELD OF THE INVENTION

[0001] The present invention relates to a cellulose ester film, andparticularly to an optical film having improved visibility by forming ametal oxide layer on a cellulose ester film.

BACKGROUND OF THE INVENTION

[0002] Further improvement of visibility has been required with higherresolution of display device. Moving image display such as liquidcrystal TV is still inferior in visibility and improvement thereof hasbeen required. Further improvement of the durability has also come to berequired with respect to outdoor use of cell phones, notebook personalcomputers and car navigation systems. An object of the present inventionis to provide an optical film provided with a metal oxide layer, whichis utilized as an anti-reflection film or an electric conductive filmfor improving visibility of display devices, having minimal appearanceof cracks and enough durability for the outdoor use thereof.Specifically, with respect to a metal oxide layer provided on acellulose ester film, which utilized preferably as a protective film ofa polarizing plate or an anti-reflection film, there were problems ofmarked coating unevenness and easy generation of cracks.

SUMMARY OF THE INVENTION

[0003] An object of the invention is to provide an optical film, when ametal oxide film is formed thereon, having minimal curl, minimal coatingunevenness and no cracks.

[0004] Another object of the invention is to provide an optical filmhaving superior visibility.

[0005] The present invention is characterized in that a dope, whichcontains a solvent including essentially no chlorine type solvent and acellulose ester, having a total acyl group substitution degree of from2.6 to 2.85 and a ratio of molecular weight distribution M_(W)/M_(n) offrom 1.0 to 3.0, is cast on a metal support, peeled off after beingdried so as to be made peelable and dried providing tension in a widthor longitudinal direction to prepare a cellulose ester film, and a metaloxide layer is formed on thus prepared film directly or through otherintervening layers.

[0006] A non-chlorinated solvent of the present invention means asolvent containing a chloride type solvent such as methylene chloride inan amount of not more than 10 weight %, preferably not more than 5weight % and most preferably 0 weight %, based on the total amount ofthe solvent. Solvents utilized are ones containing one or more solventssuch as methyl acetate, ethyl acetate, methyl acetoacetate and acetone.

[0007] A ratio of molecular weight distribution M_(W)/M_(n) exceeding3.0 is not preferred because cracks are easily caused in a metal oxidelayer. Further, a total substitution degree of an acyl group isnecessarily from 2.6 to 2.85, because cracks are easily caused at asubstitution degree of less than 2.6 and curl becomes strong at morethan 2.85, which are not preferable. Further, cracks in a metal oxidelayer formed on a cellulose ester film can be minimized by utilizing acellulose ester film which is prepared by drying while tension in thewidth or longitudinal direction is applied during the drying processafter being peeled off.

[0008] In case of dissolving cellulose ester with a solvent whichcontains essentially no chlorine type solvents, an optical film withfurther minimized appearance of cracks can be obtained by utilizing adope prepared by means of a cooled dissolution method. The reason is notclear, but it is considered that the cellulose ester solution thusprepared is stable so as to form a uniform cellulose ester film havingno local residual stress in a drying process and the cellulose esterfilm itself is hardly suffer from uneven deformation (shrinkage orexpansion) during or after the preparation process of a metal oxidelayer.

[0009] In the invention, a cellulose ester film is further preferablycontain from 0.5 to 30 weight % of an additive having not less thanthree of aromatic rings, cycloalkyl rings or cycloalkenyl rings in amolecule. The additives can be incorporated as a UV absorbent or ananti-oxidant. Thereby, crack generation is further depressed and a metaloxide layer having an uniform layer thickness is formed as well as curlgeneration is decreased.

[0010] The means to prepare a metal oxide layer is not specificallylimited and it can be prepared by a method in which a coating solutioncontaining metal oxide fine particles is coated, or by methods such asevaporation and CVD.

[0011] Specifically preferable method in the invention is one in which athin film is formed by plasma discharge treatment while supplying areactive gas to a space between electrodes under a pressure ofatmospheric pressure or the vicinity.

[0012] The plasma discharge treatment method is a method also called anormal pressure plasma method or an atmospheric pressure plasmadischarge treatment method (hereinafter, the plasma discharge treatmentunder a pressure of atmospheric pressure or the vicinity may be simplyreferred as plasma discharge treatment), and a thin film is formed on acellulose ester film by a plasma generated by means of electricdischarge while an reactive gas is supplied to the space betweenelectrodes which are placed under a pressure of atmospheric pressure orthe vicinity.

[0013] However, although the method is extremely fast in a thin filmformation speed, there was a problem of easy appearance of uneven layerthickness of a thin film layer formed in case of forming a thin filmlayer continuously on a long roll cellulose ester film.

[0014] Consequently, the inventors have found, after extensive study tosolve the problem, that it is possible to minimize crack generation in ametal oxide layer remarkably and to reduce curl of a film preparedlargely by utilizing a cellulose ester film which is prepared in such away that a dope, which contains a solvent including essentially nochlorine type solvents and a cellulose ester having a total acyl groupsubstitution degree of from 2.6 to 2.85 and a ratio of molecular weightdistribution M_(W)/M_(n) of from 1.0 to 3.0, is cast on a metal supportand peeled off after being dried so as to be made peelable and driedproviding tension in a width or longitudinal direction to prepare acellulose ester film.

[0015] Further, a thin film layer can be formed on a cellulose esterfilm continuously for a long period, and a stable optical film havingminimal appearance of cracks in a metal oxide thin film layer andsuperior durability in respect to no milky-whitening and minimallowering of electric conductivity when stored in environment of hightemperature and high humidity, has been obtained.

[0016] In the invention, a specifically preferable metal oxide layer isone formed by means of a plasma CVD (Chemical Vapor Deposition) method.According to the invention, it is possible to restrain phenomenamarkedly such as extraordinarily strong curl caused while a metal oxidelayer being formed by a plasma CVD method or cracks caused underconditions of high temperature and humidity. Further, it is superior inrespect to environment because no chlorine type solvents are used.

[0017] An optical film of the invention can be utilized as a protectivefilm of a polarizing plate, an anti-reflection film, an anti-glaringanti-reflection film, a phase transforming film, an electric conductivefilm, an anti-static film, a brightness enhancing film, an opticalcompensation film, a viewing angle enlarging film and the like. Theyield of a polarizing plate utilizing the optical film of the inventionis high. Further, a display device utilizing the polarizing plate or theoptical film can maintain superior visibility for a long period evenunder conditions of high temperature and high humidity.

[0018] In the invention, the ratio M_(W)/M_(n) of a weight averagemolecular weight (M_(W)) to a number average molecular weight (M_(n)),of cellulose ester utilized in an optical film of the invention, ispreferably not more than 3.0 and more preferably from 1.4 to 3.0,because uneven film thickness is reduced as well as durability isimproved.

[0019] Since an average molecular weight and a molecular weightdistribution of cellulose ester can be measured by use of high-speedliquid chromatography, a number average molecular weight and a weightaverage molecular weight are calculated utilizing the same and the ratiothereof can be determined. The measurement conditions are as follows:

[0020] Solvent: methylene chloride

[0021] Column: Shodex K806, K805, K803G (three columns of products byShowa Denko K. K. were utilized in a junction)

[0022] Column temperature: 25° C.

[0023] Sample concentration: 0.1 weight %

[0024] Detector: RI Model 504 (produced by GL Science Co.)

[0025] Pump: L6000 (produced by Hitachi, Ltd.)

[0026] Flow amount: 1.0 ml/min

[0027] Calibration curve: calibration curves based on 13 samples ofstandard polystyrene STK, polystyrene (manufactured by Tosoh Corp.)M_(W)=500 to 1,000,000, were utilized.

[0028] Layer thickness of an optical film used in the invention is notspecifically limited, and is generally from 10 to 500 μm and preferablyfrom 10 to 150 μm.

[0029] Among them, in case of a cellulose ester film having a thicknessof from 10 to 60 μm in which uneven layer thickness of a metal oxidelayer is easily caused, remarkable effect of the invention is observedand the invention is specifically preferably utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic diagram illustrating an example of a plasmadischarge treatment apparatus utilized for forming a metal oxide layerof the invention.

[0031]FIG. 2 is a schematic diagram illustrating an example of a plasmadischarge treatment apparatus comprising a rotating electrode and fixedelectrodes useful for forming a metal oxide thin layer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Now, cellulose ester used in the invention will be explained. Ascellulose ester of the invention, utilized is a cellulose ester in whichhydroxyl groups of the cellulose are substituted by an acyl group,especially by an acyl group having 2 to 4 carbon atoms, to an extent ofa total acyl substitution degree of from 2.60 to 2.85.

[0033] Such cellulose ester includes cellulose diacetate, cellulosetriacetate, cellulose acetatebutylate and cellulose acetatepropionate.Among them, cellulose triacetate, cellulose acetatebutylate andcellulose acetatepropionate are preferred. In these preferable celluloseesters, a substitution degree of an acetyl group of not less than 1.6 isspecifically preferred.

[0034] Cellulose as a starting material of cellulose ester is notspecifically limited, and includes cotton linter, wood pulp (originatein softwood, and in hardwood) and kenaf.

[0035] Further, each cellulose ester obtained therefrom can be utilizedin combinations at any arbitrary mixing ratio. In case of an acylatingagent is acid anhydride (acetic anhydride, propionic anhydride andbutyric anhydride) as a cellulose starting material, cellulose ester canbe prepared by an ordinary reaction procedure using an organic acid suchas acetic acid or an organic solvent such as methylene chloride in thepresence of a proton type catalyst such as sulfuric acid.

[0036] An example of a preparation method of cellulose ester is shownbelow. Cotton linter of 100 weight parts as a starting material ofcellulose was crushed, and after being added thereto with 40 weightparts of acetic acid the system was pretreated for activation at 36° C.for 20 minutes. Thereafter, 8 weight parts of sulfuric acid, 260 weightparts of acetic anhydride and 350 weight parts of acetic acid wereadded, and esterification was performed at 36° C. for 120 minutes. Thesystem was saponification ripened at 63° C. for 35 minutes after beingneutralized with 11 weight parts of 24% magnesium acetate aqueoussolution to obtain acetyl cellulose. After the system was stirred withten times of an acetic acid solution (acetic acid/water=1/1, based onweight ratio) at room temperature for 160 minutes, it was filtered anddried to obtain a purified acetyl cellulose having an acetylsubstitution degree of 2.75. The acetyl cellulose has M_(n) of 92,000,M_(W) of 156,400, and M_(W)/M_(n) of 1.7. In a similar manner, celluloseesters having different substitution degrees and M_(W)/M_(n) ratios canbe synthesized by controlling the esterification conditions of celluloseester (temperature, time and stirring) and hydrolysis conditions.

[0037] Further, cellulose ester of mixed acids can be prepared by areaction according to a method described in JP-A 10-45804 (the term,JP-A refers to unexamined and published Japanese Patent Application). Anacyl substitution degree can be measured according to the definition ofASTM-D817-96.

[0038] A number average molecular weight (M_(n)) of cellulose ester ispreferably from 70,000 to 250,000 and more preferably from 80,000 to150,000, because it provides a large mechanical strength when beingmolded and an appropriate dope viscosity.

[0039] Cellulose ester thus obtained is dissolved in a solventcontaining essentially no chlorine type solvents to prepare a viscousliquid called as a dope, and base preparation (casting of base) isperformed generally by a method called as a solution casting method.

[0040] In the invention, it is preferred to apply a method called as acooled dissolving method when cellulose ester is dissolved in solvents,because physical property of the cast film and characteristics of ametal oxide layer formed thereon are superior.

[0041] Cooled dissolving method will be explained below.

[0042] Swelling Process

[0043] In a swelling process, cellulose ester is mixed with organicsolvents so as to be swelled by the solvents. The temperature of aswelling process is preferably from −10 to 55° C. It is usuallyperformed at room temperature. The ratio of cellulose ester to organicsolvents is determined according to the concentration of a solution tobe finally obtained. Generally, the amount of cellulose ester in amixture is preferably from 5 to 30 weight %, more preferably from 8 to20 weight % and most preferably from 10 to 15 weight %. The mixture ofsolvents and cellulose ester is preferably stirred until cellulose esteris swelled sufficiently. The stirring time is preferably from 10 to 150minutes and more preferably from 20 to 120 minutes. In the swellingprocess, there may be added components other than solvents and celluloseester: a plasticizer, an anti-aging agent, a dye and a UV absorber.

[0044] Cooling Process

[0045] In a cooling process, the swelled mixture is cooled down to from−100 to −10° C. The cooling temperature is preferably a temperature atwhich the swelled mixture is solidified. The cooling speed is preferablynot less than 1° C./min, more preferably not less than 2° C./min,further more preferably not less than 4° C./min, and most preferably notless than 8° C./min. The faster is the cooling speed, the better,however, around 100° C./sec is practical. Herein, the cooling speed is avalue of the temperature difference between a temperature at start ofcooling and a final cooling temperature divided by the time durationfrom start of cooling till reaching a final cooling temperature. In acooling process, it is preferable to utilize a closed vessel to preventcontamination with water due to dewing at cooling. Further, the coolingtime can be shortened under reduced pressure. It is preferable to use apressure-resistant vessel to apply reduced pressure. Various methods orapparatuses are applicable as a concrete cooling mean.

[0046] For example, by transporting a swelled mixture with stirringthrough a cylindrical vessel while the cylinder is cooled from itssurroundings, a swelled mixture can be cooled speedily and uniformly.For that purpose, preferably utilized is an apparatus comprised of acylindrical vessel, a spiral transporting mechanism equipped in a vesselto transport a swelled mixture through the cylindrical vessel, and acooling mechanism equipped at the surroundings of a vessel to cool aswelled mixture in the vessel. Further, solvents cooled down to from−105 to −15° C. may be added into a swelled mixture to perform coolingmore speedily.

[0047] Further, a swelled mixture may be extruded as a string formhaving a diameter of from 0.1 to 20 mm into a liquid cooled at from −100to −10° C. to enable a swelled mixture to be cooled still more speedily.

[0048] Heating Process

[0049] In a heating process, a swelled mixture which has been cooled isheated. The final temperature of a heating process is usually a roomtemperature. The heating speed is preferably not less than 1° C./min,more preferably not less than 2° C./min, further more preferably notless than 4° C./min and most preferably not less than 8° C./min. Thefaster is the heating speed, the better, however, around 100° C./sec ispractical. Herein, the heating speed is a value of the temperaturedifference between a temperature at start of heating and a final heatingtemperature divided by the time duration from start of heating tillreaching a final heating temperature. The heating time can be shortenedby heating under an increased pressure. A pressure-resistant vessel ispreferably utilized to perform increased pressure. Further, whendissolution is insufficient, the process from a cooling to heatingprocess may be repeated. Whether dissolution is sufficient or not can bejudged merely by visual observation of the appearance of the solution.Various methods or apparatus are applicable as a concrete heating mean.

[0050] For example, by transporting a swelled mixture with stirringthrough a cylindrical vessel while the cylinder is heated from itssurroundings, a swelled mixture can be heated speedily and uniformly.For that purpose, preferably utilized is an apparatus comprised of acylindrical vessel, a spiral transporting mechanism equipped in a vesselto transport a swelled mixture through the cylindrical vessel, and aheating mechanism equipped at the surroundings of a vessel to heat aswelled mixture in the vessel.

[0051] Further, a swelled mixture as a string form having a diameter offrom 0.1 to 20 mm may be immersed into a liquid heated at from 0 to 55°C. to enable a swelled mixture to be heated still more speedily. In caseof applying a method, in which a swelled mixture is extruded as a stringform, in a cooling process, the string form swelled mixture may beimmersed into a liquid for heating.

[0052] Further, a swelled mixture which has been cooled may beintroduced through a cylindrical vessel, the flow of the swelled mixturebeing divided into plural flows of which direction is rotated within avessel, and the swelled mixture can be heated from the surroundings ofthe vessel while repeating the division and rotation. A vessel equippedwith partitions which causes division and rotation of substance, whichis described above, is generally known as a static type mixer. In atypical static type mixer, Kenix™ Mixer, an element which divides a flowof substance into two flows and rotate them clockwise by 180 degrees andan element which divides a flow of substance into two flows and rotatethem anti-clockwise by 180 degrees are arranged in a vessel one afteranother while being shifted by 90 degrees each other. Furthermore, aswelled mixture may be heated to a temperature of not less than theboiling point of the solvent under a pressure that is controlled toprevent the solvent from boiling. The temperature is determineddepending on the kind of a solvent, and is generally from 60 to 200° C.The pressure is determined by the relationship between the temperatureand the boiling point of the solvent.

[0053] Treatment After Solution Preparation

[0054] The solution prepared can be subjected to treatments such asconcentration adjustment (concentration or dilution), filtration,temperature adjustment and component addition, when necessary. Addingcomponents are determined depending on the purpose of a cellulose esterfilm. Typical additives are a plasticizer, an anti-degradation agent, adye and a UV-absorbent described above.

[0055] A dope thus obtained can be subjected to base film production(casting of base) by a method called as solution casting method.

[0056] In the method, a dope (cellulose ester solution) is cast througha pressure die onto a metal support for casting (hereinafter, may besimply referred as a metal support), such as an endless metal belt beingtransported infinitely (for example, a stainless steel belt) or arotating metal drum (for example, cast iron with a chromium platedsurface), and the web (a dope film) is peeled off from the support anddried to prepare a base film.

[0057] In the invention, a film obtained by being peeled off within 60seconds after casting and dried while a tension being provided isspecifically preferred because cracks are hardly generated in a metaloxide layer formed on the film.

[0058] Organic solvents utilized to prepare these dopes in the inventionare solvents containing essentially no chlorine type solvents,preferably being able to dissolve cellulose ester, and have anappropriate boiling point. They include, for example, such as methylacetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran,1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate,2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol,1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol,1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol,nitroethane, 1,3-dimethyl-2-imidazolidinone and methyl acetoacetate, andpreferable organic solvents (that is good solvents) include such asdioxolane derivatives, methyl acetate, ethyl acetate, methylacetoacetate and acetone.

[0059] A peel off tension when a web is peeled off from a metal supportfor casting is preferably not more than 300 N/m, and a transport tensionis preferably not more than 300 N/m, more preferably not more than 250N/m and still more preferably from 100 to 200 N/m.

[0060] In a drying process of the invention, a web, after being peeledoff from a metal support, is preferably dried while being provided withtension in a width or longitudinal direction so that an optical filmhaving a metal oxide layer is superior in durability. To provide tensionin a width or longitudinal direction means also an biaxial stretchingmethod in which tension is provided not in one direction but in both ofa width and a longitudinal directions. In the invention, preferred is abiaxial stretching method.

[0061] A stretching magnification of cellulose ester by a tenter ispreferably from 1.01 to 1.5 times. A residual solvent amount atstretching is preferably from 3 to 30 weight %. Thereby, durability of ametal oxide layer is also further improved.

[0062] In the invention, a residual solvent amount is defined accordingto the following equation:

Residual solvent amount (%)=[(weight of web before heat treatment−weightof web after heat treatment)/(weight of web after heat treatment)]×100

[0063] Herein, heat treatment to measure a residual solvent amount wasperformed at 115° C. for 1 hour.

[0064] A cellulose ester film of the invention preferably contains aplasticizer. The plasticizer is not specifically limited and includes aphosphate ester type plasticizer, a phthalate ester type plasticizer, atrimellitate ester type plasticizer, a pyromellitate ester typeplasticizer, a glycolate type plasticizer, a citrate ester typeplasticizer, a polyester type plasticizer, etc.

[0065] A phosphoric ester type includes, for example, such as triphenylphosphate, tricresyl phosphate, cresyl phenyl phosphate, octyl diphenylphosphate, diphenyl biphenyl phosphate, trioctyl phosphate and tributylphosphate. A phthalic ester type includes, for example, such as diethylphthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctylphthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzylphthalate and cyclohexyl phthalate. A trimellitic ester type plasticizerincludes, for example, such as tributyl trimellitate, triphenyltrimellitate and triethyl trimellitate. A pyromellitic ester typeplasticizer includes, for example, such as tetrabutyl pyromellitate,tetraphenyl pyromellitate and tetraethyl pyromellitate. A glycerin esterincludes, for example, such as triacetin and tributyrin. A glycolateester type includes, for example, such as ethylphthalylethyl glycolate,methylphthalylethyl glycolate and butylphthalylbutyl glycolate. Otherexamples of a carboxylic ester type includes polyalcohol esters such asbutyl oleinate, methylacetyl ricinolate, dibutyl sebacinate, variouskinds of trimellitate esters and trimethylolpropane tribenzoate. Amongthese, preferable are a phosphate ester type plasticizer and a glycolateester type plasticizer.

[0066] These plasticizers are preferably utilized alone or incombinations. Further, the amount of a plasticizer is preferably from 1to 30 weight % based on cellulose ester, in respect to such asperformance and processing of the film.

[0067] A UV absorbent is preferably included in a cellulose ester filmof the invention in respect to preventing a film from degradation whenit is placed outdoors as an image display device. Preferably utilized asa UV absorbent is one having superior absorbing ability of UV ray atwavelengths of not longer than 370 nm and small absorption of visiblelight at wavelengths of not shorter than 400 nm.

[0068] For example, oxybenzophenone type compounds, benzotriazol typecompounds, salicylate ester type compounds, benzophenone type compounds,cyanoacrylate type compounds, nickel complex salt type compounds andtriazine type compounds are included, however, the invention is notlimited thereto.

[0069] A benzotriazole type UV absorbent includes, for example, such as2-(2′-hydroxy-5′-methylphenyl) benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl) benzotriazole,2-(2′-hydroxy-3′-di-tert-butyl-5′-methylphenyl) benzotriazole,2-(2′-hydroxy-3′5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′-(3″,4″,5″,6″-tetrahydrophthalimidomethyl)-5′-methylphenyl)benzotriazole,2-2′-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-ile)phenol),2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole,2-(2H-benzotriazole-2-ile)-6-(straight chain and side chaindodecyl)-4-methylphenol,octyl-3-[3-tert-butyl-4-hydroxy-5-(chloro-2H-benzotrizole-2-ile)phenyl]propionate and2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazole-2-ile)phenyl] propionate; and TINUVIN 109, TINUVIN 171 and TINUVIN 326(manufactured by Ciba Specialty Chemicals Co.) which are available onthe market can be preferably used.

[0070] Further, a benzophenone type UV absorbent is also one of usefulUV absorbents for a cellulose ester film of the invention.

[0071] For example, such as 2,4-dihydroxybenzophenone,2,2′-dihydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxy-5-sulfobenzophenone andbis(2-methoxy-4-hydroxy-5-benzoylphenylmethan) are included.

[0072] In an optical film of the invention, a benzotriazole type UVabsorbent or a benzophenone type UV absorbent, which are highlytransparent and have a superior effect of preventing a polarizing plateor a liquid crystal from degradation, are preferably used; and amongthem a benzotriazole type UV absorbent having lower unnecessary coloringis specifically preferred. Further, preferable is a UV absorbent whichhardly bleeds out or evaporates in a casting process.

[0073] Further, as more preferable additives such as a plasticizer or aUV absorbent utilized in the invention, from 0.5 to 30 weight % ofadditives having not less than three of an aromatic ring, a cycloalkylring or a cycloalkenyl ring in a molecule are preferably contained, andspecifically preferable is a non-phosphoric acid type additive havingnot less than three rings selected from a benzene ring, a cyclohexanering and a cyclohexene ring in a molecule. Further, these rings may beprovided with a substituent.

[0074] In a web containing a plasticizer, which is a non-phosphoric acidtype additive having not less than three rings selected from a benzenering, a cyclohexane ring and a cyclohexene ring in a molecule, it isconsidered that minimal migration of a plasticizer from the inside tothe surface may occur during drying of the web not to be concentrated onthe surface so that there hardly remains local stress in a celluloseester film prepared by being dried while tension is applied.

[0075] A cellulose ester film, which contains a non-phosphoric acid typeadditive having not less than three rings selected from a benzene ring,a cyclohexane ring and a cyclohexene ring in a molecule, can improvewater vapor permeability and enhance stability at high temperature andhumidity.

[0076] A non-phosphoric acid type additive having not less than threerings selected from a benzene ring, a cyclohexane ring and a cyclohexenering in a molecule may contain not less than three of only benzenerings, of only cyclohexane rings, of only cyclohexene rings, and therings may be condensed rings thereof or may contain rings condensed withheterocyclic rings.

[0077] In the invention, the number of rings means individual rings of abenzene ring, a cyclohexane ring or a cyclohexene ring contained in acondensed ring. For example, a naphthalene ring counts two. The ringsmay contain a substituent. In the invention, the number of the rings ispreferably from 3 to 20, and more preferably from 3 to 10.

[0078] An additive having not less than three rings selected from abenzene ring, a cyclohexane ring and a cyclohexene ring in a moleculemore preferably utilized in the invention includes the following:

[0079] P-43: dibenzyl phthalate

[0080] P-44: dibenzyl isophthalate

[0081] P-45: dibenzyl terephthalate

[0082] P-46: diphenyl phthalate

[0083] P-47: diphenyl isophthalate

[0084] P-48: diphenyl terephthalate

[0085] P-49: dicyclohexyl phthalate

[0086] P-50: dicyclohexyl isophthalate

[0087] P-51: dicyclohexyl terephthalate

[0088] P-52: phenylcyclohexyl isophthalate

[0089] P-53: phenylcyclohexyl terephthalate

[0090] P-54: phenylcyclohexyl phthalate

[0091] P-55: benzylcyclohexyl phthalate

[0092] P-56: benzylcyclohexyl terephthalate

[0093] P-57: benzylcyclohexyl isophthalate

[0094] P-58: dibenzylcyclohexane diacetate

[0095] P-59: 1,3-cyclohexane dimethyldibenzoate

[0096] P-60: 1,3-dibenzylcyclohexane dicarboxylate

[0097] P-61: 1,2-dibenzyl teteradehydrophthalate

[0098] P-62: 1,2-dicyclohexyl teterahydrophthalate

[0099] P-63: 1,3-cyclohexylcyclohexyl dicarboxylate

[0100] P-64: glycerin tribenzoate

[0101] P-65: glycerin triphenylacetate

[0102] P-66: tribenzylacetyl acetylcitrate

[0103] P-67: tricyclohexyl citrate

[0104] P-68: methyl abietate

[0105] P-69: ethyl abietate

[0106] P-70: butyl abietate

[0107] P-71: methyl dehydroabietate

[0108] P-72: butyl dehydroabietate

[0109] P-73: methyl parastriate

[0110] etc., and low molecular weight polymers as oligomers preferablyinclude resin oligomers such as

[0111] P-74: KE-604 (manufactured by Arakawa Kagaku Co.)

[0112] P-75: KE-85 (manufactured by Arakawa Kagaku Co.)

[0113] P-76: Araldite EPN1139 (manufactured by Asahi Ciba Co., Ltd.)

[0114] P-77: Araldite GY260 (manufactured by Asahi Ciba Co., Ltd.)

[0115] P-78: Hilac 110H (manufactured by Hitachi Kasei Co., Ltd.)

[0116] P-79: Hilac 111 (manufactured by Hitachi Kasei Co., Ltd.)

[0117] however, the invention is not limited thereto, and othercompounds described in the detailed description or in the examples, canbe preferably used.

[0118] Further, additives described below is included.

[0119] These additives are preferably contained at an amount of from 0.2to 30 weight % and preferably from 1 to 20 weight %, based on acellulose ester film.

[0120] In the invention, fine particles are preferably incorporated tocontrol a kinetic friction coefficient of a cellulose ester film.

[0121] Fine particles include inorganic fine particles, for example,such as silicon dioxide, titanium dioxide, aluminum oxide, zirconiumoxide, calcium carbonate, kaolin, talk, calcined calcium silicate,hydrated calcium silicate, aluminum silicate, magnesium silicate andcalcium phosphate; polymethacrylic methyl acrylate resin powder,acrylstyrene type resin powder, polymethylmethacrylate resin powder,silicone type resin powder, polystyrene type resin powder, polycarbonateresin powder, benzoguanamine type resin powder, melamine type resinpowder, polyolefin type resin powder, polyester type resin powder,polyamide type resin powder, polyimide type resin powder orpolyfluoroethylene type resin powder; and specifically preferable arecross-linked polymer fine particles. The invention is not limitedthereto.

[0122] Among these, silicon dioxide is specifically preferred to controlkinetic friction coefficient and to be able to minimize haze of a film.A mean particle diameter of a primary particle or secondary particle ofthe fine particles is preferably within a range of from 0.01 to 1.0 μm,and the content is preferably from 0.005 to 0.5 weight % based on acellulose ester film. Silicon dioxide has been often subjected to asurface treatment with an organic substance, which is preferable becausehaze of a film can be reduced.

[0123] Preferable organic substance for a surface treatment includessuch as a halosilane series, an alkoxysilane series, a silazane andsiloxane.

[0124] Since the effect on a sliding property is large when a meanparticle diameter of fine particles is large, and on the contrary,transparency is superior when a mean particle diameter of fine particlesis small, a mean diameter of a primary particle of fine particles ispreferably not more than 20 nm, more preferably from 5 to 16 nm andspecifically preferably from 5 to 12 nm. It is preferable to formroughness of 0.01 to 1.0 μm on the surface of a cellulose ester film byadding these fine particles in a cellulose ester film.

[0125] Silicon dioxide fine particles include such as AEROSIL 200, 200V,300, R972, R972V, R974, R201, R812, OX50 and TT600 manufactured byNippon Aerosil Co., Ltd., and preferable are AEROSIL 200V, R972, R972V,R974, R202 and R812.

[0126] These fine particles may be used in combinations of two or morekinds. Any mixing ratio can be applied when being used in combinationsof two or more kinds.

[0127] In this case, fine particles of different mean particle diametersor materials, for example, AEROSIL 200V and R972 in a range of from0.1/99.9 to 99.9/0.1 based on a weight ratio can be utilized. Aszirconium oxide, for example, products available on the market such asAEROSIL 976 or R811 (manufactured by Nippon Aerosil Co., Ltd.) can beutilized.

[0128] As an organic fine particles, for example, silicone resins suchas TOSPERL 103, 105, 108, 120, 145, 3120 and 240 (manufactured byToshiba Silicone Co., Ltd.) available on the market can be alsoutilized.

[0129] In the invention, the measurement of a primary mean particlediameter of fine particles is performed by observing 100 particlesthrough a transparent type electron microscope (at a magnification offrom 500,000 to 2,000,000 times) and averaging the measured values todetermine a primary mean particle diameter.

[0130] An apparent specific gravity of fine particles is preferably notless than 70 g/l, more preferably from 90 to 200 g/l and specificallypreferably from 100 to 200 g/l. The larger the apparent specific gravitythe higher concentration of dispersion solution can be prepared, whichis preferable because of depressed haze and few coagula, and it isspecifically preferred in such a case as the invention where a dopehaving a high solid concentration is prepared.

[0131] Silicon dioxide fine particles having a mean primary particlediameter of not more than 20 nm and an apparent specific gravity of notless than 70 g/l can be prepared, for example, by burning a mixture ofvaporized silicon tetrachloride and hydrogen in the air at from 1,000 to1,200° C. In the invention, to determine an apparent specific gravitydescribed above, a given amount of silicon dioxide fine particles weretaken up in a measuring cylinder, the weight was measured andcalculation was performed according to the following equation:

Apparent specific gravity (g/l)=weight of silicon dioxide (g)/volume ofsilicon dioxide (l)

[0132] A method to prepare a dispersion solution of fine particles and amethod to add the solution to a dope in the invention, for example,include three methods described below.

[0133] (Preparation Method A)

[0134] After organic solvents and fine particles are mixed withstirring, dispersion is performed by a dispersing device to prepare adispersion solution of fine particles. The dispersion solution of fineparticles is added to a dope solution and the system is stirred.

[0135] (Preparation Method B)

[0136] After organic solvents and fine particles are mixed withstirring, dispersion is performed by a dispersing device to prepare adispersion solution of fine particles. The dispersion solution of fineparticles is added and stirred to a solution in which a small amount ofcellulose ester is added and dissolved with stirring in organic solventsseparately prepared to obtain an additive solution of fine particles.This solution is mixed sufficiently with a dope solution by use of anin-line mixer.

[0137] (Preparation Method C)

[0138] A small amount of cellulose ester is added to organic solventsand dissolved with stirring. Fine particles are added thereto anddispersion is performed by a dispersing device to prepare an additivesolution of fine particles. The additive solution of fine particles ismixed with a dope solution sufficiently by use of an in-line mixer.

[0139] Preparation method A is superior in respect to dispersibility ofsilicon dioxide fine particles, and preparation method C is superior inrespect to re-coagulation of silicon dioxide fine particles being hardlyoccur. Among them, preparation method B described above is a preferablepreparation method since it is superior in both of dispersibility ofsilicone dioxide fine particles and re-coagulation of silicon dioxidefine particles hardly being occured.

[0140] (Dispersion Method)

[0141] A concentration of silicon dioxide, when silicon dioxide fineparticles are dispersed by mixing with such as organic solvents, ispreferably from 5 to 30 weight %, more preferably from 10 to 25 weight %and most preferably from 15 to 20 weight %.

[0142] An addition amount of silicon dioxide fine particles to celluloseester is preferably from 0.01 to 0.5 weight parts, more preferably from0.05 to 0.2 weight parts and most preferably from 0.08 to 0.12 weightparts, based on 100 weight parts of cellulose ester. The larger theaddition amount the more superior in a kinetic friction coefficient of acellulose ester film, and the smaller the addition amount the moresuperior in respect to low haze as well as few coagula.

[0143] An organic solvent utilized for a dispersion solution ispreferably lower alcohols and as lower alcohols included are methanol,ethanol, propyl alcohol, isopropyl alcohol, butanol, etc., which can bepreferably used. An organic solvent other than lower alcohols is notspecifically limited and preferably an organic solvent utilized atpreparation of a dope. For example, such as methyl acetate, ethylacetate, acetone and methyl acetoacetate are utilized in preparation ofa dope.

[0144] As a dispersing device can be utilized an ordinary dispersingdevice. A dispersing device can be classified into a media dispersingdevice and a media-less dispersing device. For the purpose of dispersionof silicon dioxide fine particles is preferred the latter because hazeis lowered.

[0145] A media dispersing device includes such as a ball mill, a sandmill and a dynomill.

[0146] Further, a media-less dispersing device includes such as anultra-sonic type, a centrifugal type and a high pressure type of which ahigh pressure type is preferable in the invention, and a high pressuredispersing device is preferred.

[0147] A high pressure dispersing device is a device which providesspecific conditions such as a high share or a high pressure state bysending a mixture composition of fine particles and organic solventsthrough a fine tube at a high speed. When a treatment by use of a highpressure dispersing device is performed, it is preferred that a maximumpressure condition in the device is preferably not less than 9.8 MPa,for example, at a fine tube having a diameter of from 1 to 2,000 μm.Furthermore preferable is a pressure not less than 19.6 Mpa. In thecase, the maximum speed preferably reaches not less than 100 m/sec, andheat conducting speed preferably reaches not less than 420 kJ/hour.

[0148] High pressure dispersing devices such as described above includea high pressure homogenizer (product name: Microfluidizer) produced byMicrofluidics Corporation or Nanomizer produced by Nanomizer Co. andalso include a Manton-Gaulin type high pressure dispersing device suchas, for example, a homogenizer produced by Izumi Food Machinery andUHN-01 produced by Sanwa Kikai Co., Ltd.

[0149] In the invention, when fine particles described above areincorporated, they are preferably distributed uniformly with respect toa thickness direction of a cellulose ester film, more preferablydistributed so as to be present mainly in the vicinity of the surface,and two or more kinds of dopes are simultaneously cast, for example, bya co-casting method using one die, so that a dope containing fineparticles is arranged on the surface side. Thereby, haze is decreasedand a kinetic friction coefficient is also lowered. It is still morepreferable to arrange a dope containing fine particles at one or both ofthe surface side layers, by using three kinds of dopes.

[0150] To control a kinetic friction coefficient of a cellulose esterfilm of the invention, a back-coating layer containing fine particles isalso preferably provided on the backside of the film, and a kineticfriction coefficient can be controlled by changing such as the size,addition amount and material of fine particles.

[0151] Fine particles useful for incorporation in a back-coating layerof the invention include fine particles of an inorganic compound or anorganic compounds, and such as a kind of fine particles, a particlediameter thereof, an apparent specific gravity thereof and a dispersingmethod thereof are almost similar to those in the case of fine particlesincorporated in a cellulose ester film described above.

[0152] Addition amount of fine particles to a binder of a back-coatinglayer is preferably from 0.01 to 1 weight parts, more preferably from0.05 to 0.5 weight parts and most preferably 0.08 to 0.2 weight parts,based on 100 parts of the resin. The more the addition amount thesmaller is a kinetic friction coefficient, and the less the additionamount the lower is haze as well as the fewer is coagula.

[0153] Organic solvents utilized in a back-coating layer are notspecifically limited, however, organic solvents which dissolve acellulose ester film and a raw material resin thereof are useful becausethey provide an anti-curl function to a back-coating layer. They may beselected according to a curl degree, a kind of resin, a mixing ratio anda coating amount and the like, of a cellulose ester film.

[0154] Organic solvents which can be utilized in a back-coating layerinclude, for example, such as benzene, toluene, xylene, dioxane,acetone, methyl ethyl ketone, N,N-dimethyl formamide, methyl acetate,ethyl acetate, trichloroethylene, methylene chloride, ethylene chloride,tetrachloroethane, trichloroethane, chloroform, or N-methylpyrrolidoneand 1,3-dimethyl-2-imidazolidine.

[0155] Organic solvents which do not dissolve cellulose ester include,for example, methanol, ethanol, n-propyl alcohol, i-propyl alcohol,n-butanol, etc., however organic solvents are not limited thereto.

[0156] As a coating method for a coating composition of a back-coatinglayer, it is preferable to make a coating solution thickness (alsoreferred as a wet thickness) from 1 to 100 μm and specificallypreferable from 5 to 30 μm, by use of such as a gravure coater, a dipcoater, a wire-bar coater, a reverse coater and an extrusion coater.

[0157] Resins utilized in a back-coating layer include, for example,vinyl type homopolymers or copolymers such as a vinyl chloride/vinylacetate copolymer, a vinyl chloride resin, a vinyl acetate resin, acopolymer of vinyl acetate and vinyl alcohol, a partially hydrolyzedvinyl chloride/vinyl acetate copolymer, a vinyl chloride/vinylidenechloride copolymer, a vinyl chloride/acrylonitrile copolymer, aethylene/vinyl alcohol copolymer, a chlorinated polyvinylchloride, anethylene/vinyl chloride copolymer and a ethylene/vinyl acetatecopolymer; cellulose ester type resins such as cellulose nitrate,cellulose acetate propionate, cellulose diacetate, cellulose triacetate,cellulose acetate phthalate and cellulose acetate butylate; rubber typeresins such as a copolymer of maleic acid and/or acrylic acid, acopolymer of acrylate ester, an acrylonitrile/styrene copolymer, achlorinated polyethylene, an acrylonitrile/chlorinatedpolyethylene/stylene copolymer, a methyl methacrylate/butadiene/styrenecopolymer, an acryl resin, a polyvinylacetal resin, a polyvinylbutyralresin, a polyester polyurethane resin, a polyether polyurethane resin, apolycarbonate polyurethane resin, a polyester resin, a polyether resin,a polyamide resin, an amino resin, a styrene/butadiene resin and abutadiene/acrylonitrile resin; a silicone type resin, afluorine-containig type resin, polymethyl methacrylate, a copolymer ofpolymethylmethacrylate and polymethylacrylate; however, the invention isnot limited thereto. Specifically preferable are cellulose type resinssuch as cellulose diacetate and cellulose acetate butyrate.

[0158] A kinetic friction coefficient can be made to be not more than0.9 by providing the foregoing back-coating layer.

[0159] An optical film of the invention is characterized by that a metaloxide layer is provided on a cellulose ester film directly or throughother intervening layers, however more preferably it is formedintervening a cured resin layer or other layers.

[0160] A cured resin layer may be provided with various functions, andmay be, for example, an anti-glare layer or a clear hard coat layer. Acured resin layer is preferably prepared by polymerizing a compositioncontaining one or more kinds of ethylenically unsaturated monomers.

[0161] As a resin layer which is formed by polymerizing a compositioncontaining ethylenically unsaturated monomers, preferably utilized is alayer formed by curing an actinic ray curable resin or heat curableresin, and specifically more preferably an actinic ray curable resin.

[0162] Herein, an actinic ray curable resin layer refers to a layercomprised of a resin, which cures through such as a cross-linkingreaction by actinic ray irradiation of UV ray or electron beam, as amain component.

[0163] An actinic ray curable resin includes a UV curable resin and anelectron beam curable resin as typical examples, however, may also be aresin which cures by actinic ray irradiation other than UV and electronbeam.

[0164] A UV curable resin includes, for example, such as a UV curableacryl urethane type resin, a UV curable polyester acrylate type resin, aUV curable epoxy acrylate type resin, a UV curable polyol acrylate typeresin or a UV curable epoxy type resin.

[0165] Concrete examples, for example, include such as trimethylolpropane triacrylate, ditrimethylol propane tetracrylate, pentaerythritoltriacrylate, pentaerythritol tetracrylate, dipentaerythritolhexaacrylate and alkyl modified dipentaerythritol pentaacrylate.

[0166] A UV curable acryl urethane type resin includes generally thoseprepared easily by further reacting a acrylate type monomer having ahydroxy group such as 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate (hereinafter, only acrylate will be described as includingalso methacrylate) and 2-hydroxypropyl acrylate with a product, which isprepared by reacting an isocyanate monomer or prepolymer to a polyesterpolyol, and can be utilized those described in JP-A 59-151110.

[0167] A UV curable polyester acrylate type resin includes generallythose prepared easily by reacting a 2-hydroxyethyl acrylate or a2-hydroxy acrylate type monomer with a polyester polyol, and can beutilized those described in JP-A 59-151112.

[0168] Concrete examples of a UV curable epoxy acrylate type resininclude a product which is prepared by adding a reactive diluent and aphotoreaction initiator to epoxy acrylate as an oligomer and reactingthem, and can be utilized those described in JP-A 1-105738.

[0169] The photoreaction initiator includes concretely such as benzoineand its derivative, acetophenone, benzophenone, hydroxy benzophenone,Michler's ketone, α-amyloxim ester and thioxanthone. They may beutilized together with a photo sensitizer.

[0170] The photoreaction initiator described above can be utilized alsoas a photo sensitizer. Further, sensitizers such as n-butyl amine,triethyl amine and tri-n-butyl phosphine can be utilized when an epoxyacrylate type photoreaction agent is used.

[0171] A resin monomer, for example, include usual monomers, as amonomer having one unsaturated double bond, such as methyl acrylate,ethyl acrylate, butyl acrylate, benzyl acrylate, cyclohexyl acrylate,vinyl acetate and styrene. And as a monomer having two or moreunsaturated double bonds are included ethyleneglycol diacrylate,propyleneglycol diacrylate, divinyl benzene, 1,4-cyclohexyanediacrylate, 1,4-cyclohexyldimethyl diacrylate; and the foregoingtrimethylolpropane triacrylate and pentaerythritol tetraacrylate ester.

[0172] Products available on the market as a UV curable resin which canbe utilized in the invention may be suitably selected from AdekaoptomerKR, BY Series: KR-400, KR-410, KR-550, KR-566, KR-567 and BY-320B(manufactured by Asahi Denka Co., Ltd.); Koeihard A-101-KK, A-101-WS,C-302, C-401-N, C-501, M-101, M-102, T-102, D-102, NS-101, FT-102Q8,MAG-1-P20, AG-106 and M-101-C (manufactured by Koei Kagaku Co., Ltd.);Seikabeam PHC2210(S), PHC X-9(K-3), PHC2213, DP-10, DP-20, DP=30, P1000,P1100, P1200, P1300, P1400, P1500, P1600, SCR900 (manufactured byDainichiseika Kogyo Co., Ltd.); KRM7033, KRM7039, KRM7131, UVECRYL29201and UVECRYL29202 (manufactured by Daicel U. C. B. Co., Ltd.); RC-5015,RC-5016, RC-5020, RC-5031, RC-5100, RC-5102, RC-5120, RC-5122, RC-5152,RC-5171, RC-5180 and RC-5181 (manufactured by Dainippon Ink & Chemicals,Inc.); Aurex No.340 Clear (manufactured by Chyugoku Toryo Co., Ltd.);Sunrad H-601 (manufactured by Sanyo Kaseikogyo Co., Ltd.); SP-1509 andSP-1507 (manufactured by Syowa Kobunshi Co., Ltd.); RCC-15C(manufactured by Grace Japan Co., Ltd.) and Aronix M-6100, M-8030 andM-8060 (manufactured by Toagosei Co., Ltd.).

[0173] These actinic ray curable resin layers can be coated by a methodwell known in the art. As a light source to form a cured layer from a UVcurable resin by photo-curing reaction, there is no limitation for useas far as a light source generates UV ray. For example, such as alaw-pressure mercury lamp, a medium-pressure mercury lamp, ahigh-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a carbonarc lamp, a metal halide lamp and a xenon lamp can be utilized. Theirradiation conditions may change depending on each lamps, however, anirradiation quantity of light is preferably approximately from 20 to10,000 mJ/cm² and more preferably from 50 to 2,000 mJ/cm². A curedlayer, when it is formed at a range from near UV to visible light, canbe efficiently formed by use of a sensitizer having the maximumabsorption within a range thereof.

[0174] As organic solvents for a coating solution of a UV curable resinlayer composition, can be utilized, for example, a solvent suitablyselected from a hydrocarbon series, an alcohol series, a ketone series,a ester series, a glycol ether series and other organic solvents, orcombinations thereof. It is preferred to utilize an organic solventdescribed above containing not less than 5 weight % of and morepreferably from 5 to 80 weight % of such as propyleneglycolmonoalkylether (having 1 to 4 carbon atoms of an alkyl group) orpropyleneglycol monoalkylether acetate ester (having 1 to 4 carbon atomsof an alkyl group).

[0175] As a coating method for a coating solution of UV curable resincomposition can be utilized the methods described above. A coatingamount is suitably from 0.1 to 30 μm and preferably from 0.5 to 15 μm,as a wet layer thickness.

[0176] A UV curable resin composition is preferably irradiated by UV rayduring or after coating and drying. The irradiation time is preferablyfrom 0.5 seconds to 5 minutes and more preferably from 3 seconds to 2minutes in respect to efficient curing or operation efficiency.

[0177] To a cured resin layer thus obtained, may be added fine particlesmade of an inorganic or organic compound to prevent blocking, to enhanceabrasion resistance or to provide anti-glare property, and the kind isalmost similar to the fine particles of a matting agent described above.

[0178] A mean particle diameter of the fine particles is preferably from0.005 to 5 μm and specifically preferably from 0.01 to 1 μm.

[0179] The ratio of fine particle powder to a UV curable resincomposition is preferably from 0.1 to 10 weight parts based on 100weight parts of a resin composition.

[0180] A UV curable resin layer may be a clear hard coating layer havinga mean center-line roughness (Ra) of from 1 to 50 nm or a anti-glarelayer having a Ra of from 0.1 to 1 μm.

[0181] In the invention, a metal oxide thin layer can be formed on theselayers.

[0182] Metal Oxide Thin Layer

[0183] In the invention, a method to provide a metal oxide layer is notspecifically limited and the layer can be formed by coating, spattering,evaporation and CVD (Chemical Vapor Deposition) method.

[0184] A method to form a metal oxide layer by coating includes such asa method in which metal oxide powder is dispersed in a binder resinhaving been dissolved in solvents, coated and dried; a method in which apolymer having a cross-linking structure is utilized as a binder resin;and a method in which an ethylenically unsaturated monomer and aphotopolymerization initiator being included in a system, which isirradiated by actinic ray to form a layer.

[0185] In the invention, it is indispensable to form a metal oxide layeron a cellulose ester film or on a cellulose ester film provided withsuch as a hard-coat layer. It is preferable for decreasing thereflectance to form a metal oxide layer having a law refractive index asthe top layer on a cellulose ester film and to form a high refractiveindex layer between them, or to further provide a medium refractiveindex layer (by changing an amount of a metal oxide or kind of a metal)between a cellulose ester film and a high refractive index layer. Arefractive index of a high refractive index layer is preferably from1.55 to 2.30 and more preferably from 1.57 to 2.20. A refractive indexof a medium refractive index layer is controlled so as to be anintermediate value between a refractive index of a cellulose ester filmand that of a high refractive index layer. A refractive index of amedium refractive index layer is preferably from 1.55 to 1.80. Athickness of a metal oxide layer is preferably from 5 nm to 100 μm, morepreferably from 10 nm to 10 μm and most preferably from 30 nm to 1 μm. Ahaze of a metal oxide layer is preferably not more than 5%, morepreferably not more than 3% and most preferably not more than 1%. Astrength of a metal oxide layer is preferably not less than H, morepreferably not less than 2H and most preferably not less than 3H, basedon a pencil hardness at a weight of 1 kg. In case of a metal oxide layerbeing formed by coating, inorganic fine particles and a binder polymerare preferably incorporated therein.

[0186] Fine particles utilized in a metal oxide layer and a mediumrefractive index layer preferably have a refractive index of from 1.80to 2.80 and more preferably from 1.90 to 2.80. A weight average diameterof a primary particle of inorganic fine particles is preferably from 1to 150 nm, more preferably from 1 to 100 nm and most preferably from 1to 80 nm. A weight average diameter of inorganic fine particles in alayer is preferably from 1 to 200 nm, more preferably from 5 to 150 nm,furthermore preferably from 10 to 100 nm and most preferably from 10 to80 nm. A mean particle diameter is measured by a light scattering methodwhen it is not smaller than from 20 to 30 nm, and by electron micrographwhen it is not larger than from 20 to 30 nm. A specific surface area ofinorganic fine particles is preferably from 10 to 400 m²/g, morepreferably from 20 to 200 m²/g and most preferably from 30 to 150 m²/g,as a value measured by BET method.

[0187] Inorganic fine particles are particles comprised of an oxide of ametal. Examples of an oxide or sulfide of a metal include such astitanium dioxide (e.g. rutile, mixed crystal of rutile/anatase, anatase,amorphous structure), tin oxide, indium oxide, zinc oxide and zirconiumoxide. Among them, titanium dioxide, tin oxide and indium oxide arespecifically preferred. Inorganic fine particles can include otherelements in addition to these metal oxides which is a main component. Amain component means a component of the largest content (weight %) whichcomposes particles. Examples of other elements include Ti, Zr, Sn, Sb,Cu, Fe, Mn, Pb, Cd, As, Cr, Hg, Zn, Al, Mg, Si, P and S.

[0188] Inorganic fine particles may be surface treated. Surfacetreatment can be performed by use of an inorganic compound or an organiccompound. Examples of an inorganic compound utilized for the surfacetreatment include alumina, silica, zirconium oxide and iron oxide. Amongthem, alumina and silica are preferred. Examples of an organic compoundutilized for the surface treatment include polyol, alkanol amine,stearic acid, a silane coupling agent and a titanate coupling agent.Among them, a silane coupling agent is most preferable. The surfacetreatment may be performed in combinations of two or more kinds ofsurface treatment. The form of inorganic fine particles is preferably arice shape, a spherical shape, a cubic shape, a cone shape or anirregular shape. Not less than two kinds of inorganic fine particles maybe utilized in combinations in a metal oxide layer.

[0189] The ratio of inorganic fine particles in a metal oxide layer ispreferably from 5 to 65 volume %, more preferably from 10 to 60 volume %and further more preferably from 20 to 55 volume %.

[0190] Inorganic fine particles are supplied to a coating solution forforming a metal oxide layer, as a dispersion state of being dispersed ina medium. As a dispersion medium for inorganic fine particles,preferably is utilized liquid having a boiling point of from 60 to 170°C. Concrete examples of a dispersion medium include water, alcohols(e.g. methanol, ethanol, isopropanol, butanol and benzyl alcohol),ketones (e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone andcyclohexanone), esters (e.g. methyl acetate, ethyl acetate, propylacetate, butyl acetate, methyl formate, ethyl formate, propyl formateand butyl formate), aliphatic hydrocarbons (e.g. hexane andcyclohexane), aromatic hydrocarbons (e.g. benzene, toluene and xylene),amides (e.g. dimethylformamide, dimethylacetoamide andn-methylpyrrolidone), ethers (e.g. diethyl ether, dioxane andtetrahydrofuran) and alkoxyalcohols (e.g. 1-methoxy-2-propanol). Amongthem, specifically preferable are toluene, xylene, methyl ethyl ketone,cyclohexanone and butanol.

[0191] Inorganic fine particles can be dispersed in a medium by use of adispersing device. Examples of a dispersing device include a sandgrinder mill (e.g. pin attached beads mill), a high-speed impeller mill,a pebble mill, a roller mill, an atliter and a colloidal mill.Specifically preferable are a sand grinder mill and a high-speedimpeller mill. Further a preliminary dispersion treatment may beperformed. Examples of a dispersion device for the preliminarydispersion treatment include a ball mill, a tree-rolls mill, a kneaderand an extruder.

[0192] A metal oxide layer preferably utilizes a polymer having across-linking structure (hereinafter, may be also referred as “across-linking polymer”) as a binder polymer. Examples of a cross-linkingpolymer include cross-linked products of such as, a polymer having asaturated hydrocarbon chain such as polyolefin (hereinafter, genericallyreferred as “polyolefin”), polyether, polyurea, polyurethane, polyester,polyamine, polyamide and melamine resin. Among them, preferable arecross-linked products of polyolefin, of polyether and of polyurethane,more preferable are cross-linked products of polyolefin and of polyetherand most preferable is a cross-linked product of polyolefin. Further, itis more preferable that a cross-linking polymer provided with an anionicgroup. An anionic group functions to maintain the dispersed state ofinorganic fine particles and a cross-linking structure provides apolymer with film forming ability which functions to strengthen a film.The anionic group described above may be bonded directly or through aconnecting group to a polymer chain, however, it is preferably bonded toa main chain as a side chain through a connecting group.

[0193] In the invention, a method of forming a metal oxide layer bymeans of plasma discharge treatment is specifically preferably utilized.

[0194] In what follows, a method of forming a metal oxide layer by meansof plasma discharge treatment will be explained according to FIGS. 1 and2.

[0195] Plasma discharge treatment in atmospheric pressure or in nearatmospheric pressure, as a method for forming a metal oxide layer of theinvention, is performed by utilizing such as the following plasmadischarge apparatus.

[0196]FIG. 1 illustrates an example of a plasma discharge treatmentapparatus being utilized for forming a metal oxide layer of theinvention.

[0197] In FIG. 1, the apparatus is provided with a pair of rotatingelectrodes 10A and 10B, to one of which an electric source 80 which canapply voltage for generating plasma discharge is connected through avoltage supply device 81 and to another an earth is connected through 82which is grounded.

[0198] Rotating electrodes 10A and 10B transport a cellulose ester filmbeing rotated around them, and are preferably roll electrodes orbelt-form electrodes. In FIG. 1, roll electrodes are illustrated.

[0199] The gap (electrode gap) of the roll electrodes is a place whereelectric discharge is performed, and is adjusted so that cellulose esterfilm F can be transported through. The gap between electrodes formselectric discharge portion 50.

[0200] The electrode gap is maintained under a pressure of atmosphericpressure or the vicinity and hereto reactive gas G is supplied from areactive gas supply portion 30 to perform plasma discharge treatment onthe surface of cellulose ester film F.

[0201] Herein, cellulose ester film F unwounded from a master roll orcellulose ester film F transported from a previous process istransported firstly while contacting rotating electrode 10A which isrotating in a transport direction and passes through electric dischargeportion 50 to form a thin layer on the surface of cellulose ester filmF.

[0202] Cellulose ester film F which once comes out of electric dischargeportion 50 is U-turned by U-turn rolls 11A to 11D, next beingtransported while contacting rotating electrode 10B which is rotating ina opposite direction, and passes through again the aforementionedelectric discharge portion 50 to form a thin layer by plasma dischargetreatment further onto the surface of cellulose ester film having beenprovided with a thin layer previously. The U-turn is performed usuallyin approximately from 0.1 second to 1 minute.

[0203] Reactive gas G having been used for the treatment is evacuatedthrough gas outlet 40 as exhausted gas G′. Reactive gas G is preferablysupplied to electric discharge portion 50 by heating at a temperaturefrom room temperature to 250° C., preferably from 50 to 150° C. and morepreferably from 80 to 120° C.

[0204] Further, electric discharge portion 50 is preferably equippedwith rectifying plate 51 in order to make the flow of reactive gas G andexhausted gas G′ smooth as well as to control electric discharge portion50 not to spread and generate unnecessary electric discharge betweenelectrodes 10A and 10B, and rectifying plate 51 is preferably made of aninsulating material.

[0205] A thin layer formed on cellulose ester film F is abbreviated inthe figure. Cellulose ester film F having being provided with a thinlayer on the surface thereof is transported to a direction toward awinding roll (not shown in the figure) or next process via guide roll21.

[0206] Therefore, cellulose ester film F is plasma discharge treatedwhile going and returning in electric discharge portion 50 being tightlycontact with rotating rolls 10A and 10B.

[0207] Incidentally, although not shown in the figure, devices includingsuch as rotating electrodes 10A and 10B, guide rolls 20 and 21, U-turnrolls 11A to 11D, reactive gas supply portion 30 and gas evacuationoutlet 40 are preferably surrounded by and installed in a plasmadischarge treatment vessel which shields devices from external field.

[0208] Further, although it is not shown in the figure, a temperaturecontrol medium for temperature control of rotating electrodes 10A and10B is circulated when necessary and the surface temperature of eachelectrode is controlled to a prescribed value.

[0209]FIG. 2 shows an example of a plasma discharge treatment apparatusequipped with a rotating electrode and fixed electrodes which are usefulfor forming a metal oxide thin layer of the invention.

[0210] A rotating electrode 110 and plural number of fixed electrodes111 which are arranged to face thereto are provided; cellulose esterfilm F transported from a master roll or from a previous process, whichare not shown in the figure, is guided to rotating electrode 110 througha guide roll 120 and a nip roll 122, being further transported incontact with rotating electrode 110 while being synchronized with therotation of rotating electrode 110; and reactive gas G, which isprepared in reactive gas generator 131, is supplied from air supply tube130 to electric discharge portion 150 placed under a pressure ofatmospheric pressure or the vicinity to form a thin layer on the surfaceof a cellulose ester film which is facing to fixed electrodes 111.

[0211] Rotating electrode 110 and fixed electrodes are connected on theone hand with electric source 180 via voltage supply mean 181 and on theother to an earth via 182 which is grounded.

[0212] Further, rotating electrode 110, fixed electrodes 111 andelectric discharge portion 150 are covered with plasma dischargetreatment vessel 190 to be shielded against external field. Exhaustedgas G′ having been used is evacuated through gas outlet 140 which isplaced at the bottom of a treatment chamber.

[0213] Cellulose ester film F which has been subjected to plasmadischarge treatment is transported to next process or to a wind-up roll,which is not shown in the figure, via nip roll 123 and guide roll 121.

[0214] Partition plates 124 and 125 against external field are providedat the place of nip rolls 122 and 123 in the portions where celluloseester film F comes into and goes out from a plasma discharge treatmentvessel so as to shut out the air which comes in being accompanied withnip roller 122 and cellulose ester film F from external field andfurther so as to prevent reactive gas G or exhausted gas G′ fromescaping to external field at the outlet. Incidentally, although it isnot shown in the figure, a medium with a controlled temperature fortemperature control of rotating electrodes 110 and fixed electrodes 111is circulated inside when necessary.

[0215] In this manner, in the invention, a cellulose ester film, onwhich a thin layer is formed, is preferably subjected to plasmadischarge treatment while being transported on the rotating electrode.

[0216] The surface where a rotating electrode contact with a celluloseester film is required to have high smoothness, and a surface roughnessof the surface of a rotating electrode is preferably not more than 10μm, more preferably not more than 8 μm and specifically preferably notmore than 7 μm, based on the maximum height (R_(max)) of surfaceroughness defined by JIS-B-0601. Further, it is necessary to protectelectrodes from dust or foreign matter to adhere for a uniform filmpreparation.

[0217] The surface of an electrode utilized in the invention isdesirably covered with a solid dielectric, and specifically desirablycovered with a solid dielectric with respect to electric conductive basematerials such as a metal. A solid dielectric includes plastics such aspolytetrafluoroethylene and polyethylene terephthalate; metal oxidessuch as glass, silicon dioxide, aluminum oxide (Al₂O₃), zirconium oxide(ZrO₂) and titanium dioxide (TiO₂); and double oxides such as bariumtitanate.

[0218] Specifically preferred is a ceramic covered dielectric which ispore sealing processed by use of an inorganic material after sputteringof a ceramic. Herein, electric conductive base materials such as a metalinclude metals such as silver, platinum, stainless steel, aluminum andiron, and among them preferable is stainless steel in respect tomanufacturing.

[0219] Further, as a lining material, utilized are silicate type glass,borate type glass, phosphate type glass, germanate type glass, telluritetype glass, aluminate type glass and vanadate type glass, and among themmore preferably utilized is borate type glass in respect to easymanufacturing.

[0220] In the invention, electrodes can be heated or cooled from theback side (inside), when necessary. In case of an electrode is a belt,it may be cooled by air from the back side, however, in case of arotating electrode utilizing a roll, temperature of the surface of anelectrode and of a cellulose ester film is preferably controlled bysupplying a medium inside the electrode.

[0221] As a medium, utilized preferably are distilled water, oil, andspecifically insulating materials such as silicone oil.

[0222] The temperature of a cellulose ester film at electric dischargetreatment is preferably not higher than from room temperature to 200°C., more preferably not higher than from room temperature to 120° C. andmore preferably from 50 to 110° C.

[0223] Further, significant curl may be generated such as because thetemperature of the surface of a cellulose ester film is raised also byelectric discharge, however, according to the invention, curl generationhas been markedly reduced.

[0224] Temperature unevenness of the cellulose ester film surfacespecially in a width direction at electric discharge treatment ispreferably minimized, and preferably depressed within not more than +5°C., more preferably within not more than ±1° C. and specificallypreferably within not more than ±0.1° C.

[0225] In the invention, the electrode gap distance is determined inconsideration of such as thickness of a solid dielectric, suppliedvoltage and frequency, and a purpose of plasma application. The shortestdistance between a solid dielectric and an electrode in case ofproviding one of the foregoing electrodes with a solid dielectric, orthe distance between each other solid dielectrics in case of providingboth of the foregoing electrodes with a solid dielectric, in eithercase, is preferably from 0.5 to 20 mm and specifically preferably 1±0.5mm, in respect to generate uniform plasma discharge.

[0226] In the invention, at an electric discharge portion comprised ofan electrode gap, a gas mixture generated in a gas generating device isintroduced, with regulation of the flow rate from a reactive gas supplyinlet to a plasma discharge portion. The concentration and flow rate ofa reactive gas are adjusted suitably, and are preferably supplied at asufficient rate against transportation speed of a cellulose ester film.It is preferable to set up a flow rate and electric discharge conditionsso that almost all the reactive gas supplied is consumed to react andform a thin layer.

[0227] To prevent the atmosphere from invading into an electricdischarge portion and a reactive gas from leaking out of the apparatus,it is preferable that electrodes and a cellulose ester film duringtransportation are covered as a whole to be shielded from an externalfield. In the invention, the pressure of an electric discharge portionis maintained at atmospheric pressure and the vicinity. Further, areactive gas may produce metal fine particles of a metal oxide by beingdecomposed in air-phase, and it is preferred to set up a flow rate andelectric discharge conditions so as to depress such production.

[0228] Herein, atmospheric pressure and the vicinity means a pressurefrom 20 to 200 kPa, and preferably from 93 to 110 kPa to suitably obtainthe effects described in the invention. The pressure at an electricdischarge portion is preferably a slightly plus pressure againstatmospheric pressure at outside of the apparatus, and more preferablyatmospheric pressure +0.1 to +5 kPa.

[0229] In a plasma discharge treatment apparatus useful for theinvention, it is preferable to generate stable plasma that one ofelectrodes is connected to an electric power source to be applied withvoltage and the other electrode is grounded by connecting to an earth.

[0230] The voltage value applied by a high-frequency electric powersource utilized in the invention is suitably determined; for example, avoltage is approximately from 0.5 to 10 kV, an applied frequency numberis adjusted to from 1 kHz to 150 kHz and a wave shape may be ofpulse-waves or sine-waves. Specifically preferable is to adjust thefrequency number to over 100 kHz and not more than 50 MHz to obtain apreferable electric discharge portion (electric discharge space).

[0231] Electric discharge density at an electric discharge portion ispreferably from 5 to 1,000 W·min/m² and specifically desirably from 50to 500 W·min/m².

[0232] A plasma discharge treatment portion is desirably surroundedsuitably by a treatment vessel made of Pyrex glass (R), a metal vesselalso can be used provided that against an electrode is assured. Forexample, polyimide resin may be pasted up on the inside surface of astainless steel frame, or the metal frame may be subjected to ceramicspattering to keep insulation. Further, the side surface of an electricdischarge portion and a rotating electrode and the side surface of atransportation portion of a cellulose ester film may be surrounded toenable suitably to supply a reactive gas to an electric dischargeportion or to evacuate an exhausted gas from that.

[0233] A reactive gas utilized in a method for forming a metal oxidethin layer of the invention will be explained. A reactive gas forforming a thin layer preferably contains nitrogen or a rare gas.

[0234] That is, a reactive gas is preferably a gas mixture of nitrogenor a rare gas, and the reactive gas described below.

[0235] Herein, a rare gas is an element of 18 group of the periodictable, concretely, such as helium, neon, argon, xenon and radon, andamong them preferably utilized in the invention are helium and argon.They may be used in combinations, and, for example, at a ratio of suchas helium 3 to argon 7.

[0236] Concentration of a rare gas in a reactive gas is preferably notless than 90 volume % to generate stable plasma discharge, and desirablyfrom 90 to 99.99 volume %.

[0237] A rare gas is utilized to generate stable plasma discharge, and areactive gas being ionized or radicalized is accumulated or attached onthe surface of a base material to form a thin layer.

[0238] As a reactive gas useful for the invention, a gas added with areactive gas of various substances is utilized to enable thin layershaving various functions to be formed on a cellulose ester film.

[0239] For example, by utilizing a fluorine-containing organic compoundand a silicon compound as a reactive gas, a low refractive-index layerof an anti-reflection layer can be formed.

[0240] Further, by utilizing an organometallic compound, metalhydrogencompound or metal halogenide, which includes Ti, Zr, In, Sn, Zn, Ge, Sior other metals, such as a metal oxide layer or a metal nitride layercan be formed, and these layers may function as a medium refractiveindex layer or a high refractive-index layer of an anti-reflectionlayer, as well as an electric conductive layer or an anti-static layer.

[0241] Further an anti-staining layer and a low refractive index layercan be formed by use of a fluorine-contained organic compound, and agas-barrier layer and a low refractive index layer can be formed by useof a silicon compound. The invention is utilized specifically preferablyfor preparation of an anti-reflection layer which is formed byaccumulating multi-layers of a high, medium refractive index layer and alow refractive index layer alternately.

[0242] The thickness of a metal oxide layer formed in the invention ispreferably obtained in a range from 1 to 1,000 nm.

[0243] In atmospheric pressure plasma treatment, fluorine-containedcompound including layer can also be formed by utilizing afluorine-contained organic compound as a starting gas.

[0244] Fluorine-contained organic compounds are preferably such as acarbon fluoride gas and a hydrocarbon fluoride gas.

[0245] Concretely, fluorine-contained organic compounds include, forexample, carbon fluoride compounds such as carbon tetrafluoride, carbonhexafluoride, tetrafluoroethylene, hexafluoropropyrene,octafluorocyclobutane; hydrocarbon fluoride compounds such asdifluoromethane, tetrafluoroethane, tetrafluoropropyrene,trifluoropropyrene and octafluorocyclobutane; further, halogenides of ahydrocarbon fluoride compound such as monochlorotrifluoromethane,monochlorodifluoromethane and dichlorotetrafluorocyclobutane; andfluoride-substituents of organic compounds such as alcohol, acid andketone.

[0246] They may be used alone or in combinations.

[0247] Further, these compounds may provided with an ethylenicallyunsaturated group in a molecule. The foregoing compounds can be usedalso in combinations.

[0248] In case of utilizing a fluorine-contained organic compound as areactive gas useful for the invention, a content of a fluorine-containedorganic compound as a reactive gas in a reaction gas is preferably from0.01 to 10 volume % and more preferably 0.1 to 5 volume %, in respect toforming a uniform thin layer on a cellulose ester film by plasmadischarge treatment.

[0249] Further, in case that a fluorine-contained organic compound,which is utilized preferably in the invention, is a gas under ordinarytemperatures and pressures, it can be used as it is as a component of areactive gas.

[0250] Further, in case that a fluorine-contained organic compound is aliquid or solid under ordinary temperatures and pressures, it may beused, for example, by being vaporized by means of such as heat orreduced pressure, or by being dissolved in a suitable organic solvent.

[0251] As a silicon compound as a reactive gas useful in the invention,for example, organometallic compounds such as dimethylsilane andtetramethylsilane; metal hydrogen compounds such as monosilane anddisilane; metal halogenide compounds such as dichlorosilane,trichlorosilane and tetrafluorosilane; alkoxy silanes such astetramethoxy silane, tetraethoxy silane, tetrapropoxy silane,dimethyldiethoxy silane, methyltrimethoxy silane and ethyltriethoxysilane; and organosilanes can be preferably utilized, however, theinvention is not limited thereto.

[0252] Further they can be utilized suitably in combinations. Otherorganic compounds may also be added to change or control physicalproperty of a layer.

[0253] In the invention, in case of utilizing silicon compound as areactive gas, a content of a silicon compound as a reactive gas in areaction gas is preferably from 0.01 to 10 volume % and more preferably0.1 to 5 volume %, in respect to forming a uniform thin layer on acellulose ester film by plasma discharge treatment.

[0254] A organometallic compound as a reactive gas useful in theinvention is not specifically limited and includes metal compounds toform metal oxides of, such as Al, As, Au, B, Bi, Sb, Ca, Cd, Cr, Co, Cu,Fe, Ga, Ge, Hg, In, Li, Mg, Mn, Mo, Na, Ni, Pb, Pt, Rh, Se, Si, Sn, Ti,Zr, Y, V, W and Zn.

[0255] For example, to form a high refractive index layer of ananti-reflection layer, a titanium compound is preferred and it includes,concretely, for example, organic amino metallic compounds such astetradimethylamino titanium, metal hydrogen compounds such as monotitaneand dititane, metal halogenides such as dichlorotitane, trichlorotitaneand tetrachlorotitane, and metal alkoxides such as tetraethoxy titane,tetraisopropoxy titane and tetrabutoxy titane.

[0256] In the invention, a silicon compound and an organometalliccompound is preferably a metal hydrogen compound or a metal alkoxide inrespect to handling, and among them is preferably utilized is a metalalkoxide because of no generation of a corrosive or poisonous gas andminimal contamination of the process.

[0257] In the invention, in case of utilizing an organometallic compoundas a reactive gas, a content of a organometallic compound as a reactivegas in reaction gas is preferably from 0.01 to 10 volume % and morepreferably 0.1 to 5 volume %, in respect to forming a uniform thin layeron a cellulose ester film by plasma discharge treatment.

[0258] Further, to introduce a metal compound such as a silicon compoundand a titanium compound to an electric discharge portion, both of themcan be used in any state of gas, liquid or solid under ordinarytemperatures and pressures.

[0259] In case of gas, it can be introduced to an electric dischargeportion as it is, however, in case of liquid or solid it can be utilizedby being vaporized by use vaporization means such as heat, reducedpressure and ultrasonic irradiation.

[0260] In case of utilizing an organometallic compound such as atitanium compound being vaporized by means of heat, a metal alkoxidesuch as tetraethoxy silane and tetrapropoxy silane which is liquid atordinary temperatures and has a boiling point of not higher than 200° C.is preferred to form a metal oxide thin layer of the invention.Alkoxides described above may be utilized by diluting with organicsolvents and as an organic solvent such as methanol, ethanol andn-hexane or the mixed organic solvent thereof can be used.

[0261] Further, physical property such as hardness and density of a thinlayer can be controlled by including such as oxygen, hydrogen, carbondioxide, carbon monoxide, nitrogen, nitrogen dioxide and nitrogenmonoxide in a reactive gas at a content of from 0.1 to 10 volume %.

[0262] An amorphous metal oxide layer comprised of such as silicon oxideand titanium oxide can be preferably prepared according to the foregoingmethod.

[0263] An optical film of the invention can be preferably utilized for,for example, an optical film having an anti-reflection layer comprisedof accumulated layers of a low refractive index layer and a highrefractive index layer, or an optical film having an electric conductivelayer or a anti-static layer.

[0264] In the invention, multiple thin layers can be preparedcontinuously and a multi-layered accumulated material having nounevenness of a thin layer can be prepared, by providing plural plasmadischarge apparatuses.

[0265] For example, in case of preparing an optical film having ananti-reflection layer on a cellulose ester film, it can be preparedefficiently by accumulating, a high refractive index layer having arefractive index of from 1.6 to 2.3 and a low refractive index layerhaving a refractive index of from 1.3 to 1.5, continuously on thesurface of a cellulose ester film.

[0266] A low refractive index layer is preferably a fluorine-containedcompound including layer which is formed by plasma discharge treatmentutilizing a gas containing a fluorine-contained organic compound or alayer containing mainly silicon oxide which is formed by plasmadischarge treatment utilizing an organic silicon compound such asalkoxysilane; and a high refractive index layer is preferably a metaloxide layer which is formed by plasma discharge treatment utilizing agas containing an organic metal compound, for example, a layer includingtitanium oxide or zirconium oxide.

[0267] There are utilized thin layer forming methods described above,however, the invention is not limited thereto and neither the layerconstitution is limited thereto. For example, an anti-stain layer may beformed on the outermost surface by plasma discharge treatment under thepresence of a fluorine-contained organic compound gas and underatmospheric pressure or the vicinity.

[0268] In the invention, according to the method described above, amulti-layered thin layer can be accumulated to obtain a uniform opticalfilm having no uneven thickness of each layer.

[0269] A thickness of a thin layer such as a metal oxide layer isdetermined by preparing a cross section of an accumulated material andobserving through a transmission electron microscope (hereinafter,referred as TEM)

[0270] The preparation of a cross section can be performed, concretely,by burying an accumulated material together with a base material in anepoxy burying resin for pre-treatment of electron microscopeobservation; followed by preparing a ultra-thin slice having a thicknessof approximately 80 nm by use of a ultra-microtome equipped with adiamond knife or by cutting out a thin sliced cross section having athickness of approximately 100 nm by means of focused scanning of Ga ionbeam on the surface of an accumulated material using a focused ion beam(FIB) processing apparatus.

[0271] The observation by TEM is performed at a magnification of from50,000 to 500,000 times with respect to bright ground images, and imagesare recorded on a film, imaging plate or CCD camera.

[0272] An acceleration voltage of TEM is preferably from 80 to 400 kVand specifically preferably from 80 to 200 kV.

[0273] Further, details of observation techniques of electron-micrographand preparation techniques of sample preparation can be referred to“Observation methods of electron-micrograph in medical science andbiology, edited by Kanto-shibu of Japan electron-micrograph society”(published by Maruzen), “Preparation methods of biological samples forelectron-micrograph, edited by Kanto-shibu of Japan electron-micrographsociety” (published by Maruzen) and “Electron-micrograph Q&A” (publishedby Agneshyofu Co.), respectively.

[0274] TEM images recorded on a suitable medium is decomposed into1024×1024 pixels, preferably 2048×2048 pixels, per one sheet of animage, and preferably subjected to image processing by a computer.

[0275] Details of image processing technology can be referred to“Application technology of image processing, edited by Hiroshi Tanaka(published by Kogyo-chosakai)”, and image processing programs orapparatuses are not specifically limited, provided that operationsdescribed above is possible, and an example thereof includes an imageprocessing software Image-Pro PLUS, produced by MEDIA CYBERNETICS Co.

[0276] To perform an image processing, an analogue image recorded on afilm is converted to a digital image by such as a scanner, andpreferably subjected optionally to shading correction, contrast/edgeenhancement. Thereafter, a histogram is formed, and portionscorresponding to an interface of an accumulated material is extracted bybinarization process to measure the thickness between the interfaces.

[0277] In a similar manner, a mean layer thickness and the variation canbe calculated from the values obtained for not less than 25 points andpreferably not less than 50 points.

[0278] In this way, the invention can provide optical films providedwith a metal oxide compound layer having various functions.

[0279] According to the invention, an optical film having a metal oxidelayer with markedly improved crack generation can be provided, and theoptical film showed minimal curl and depressed degradation ofperformances caused such as by decreased electric conductivity ormilky-whitening even under repeated exposure to conditions of hightemperature and humidity. Further, the invention can provide an opticalfilm having markedly depressed uneven layer thickness (coatingunevenness).

[0280] An optical film of the invention is useful specifically as aprotective film of a polarizing plate, and a polarizing plate can beprepared by utilization thereof according to a method well known in theart.

[0281] A polarizing plate which is provided with the optical film, or adisplay device provided with the optical film is superior in visibilityand has been successful in providing superior visibility even underextreme environment.

[0282] An optical film of the invention is preferably utilized for suchas an anti-reflection film, an anti-static film, a phase deference film,an electric conductive film, an electromagnetic wave shielding film, aprotecting film of such as a polarizing plate, an optical compensationfilm, a vision range widening film, a polarizing plate and a frontfilter of a plasma display.

[0283] Further, an optical film of the invention is preferably utilizedin liquid crystal display devices of a reflection-type, atransmission-type and a semi-transmission type; or in liquid crystaldisplay devices of various operating methods of such as TN-type,STN-type, OCB-type, HAN-type, VA-type and IPS-type; and also can beutilized in various display devices such as a plasma display device, anorganic EL display device and an inorganic EL display device.

EXAMPLES

[0284] The invention will be concretely explained according to examplesas follows; however, embodiments of the invention are not limitedthereto.

Example 1

[0285] Each cellulose ester shown in Table 1 (TAC1 to TAC8) was preparedaccording to an ordinary method.

[0286] Preparation of Dope A1: Cooled Dissolution

[0287] Raw materials described below were charged in a closed vessel,stirred at 30° C. for 20 min., and after the mixture was cooled down to−75° C. it was heated up to 45° C. to obtain a transparent dope. Afterbeing subjected to a defoaming operation, the solution was filteredthrough Azumi Filter Paper No. 244 produced by Azumi Roshi Co., Ltd. toprepare dope A1. Cellulose ester (TAC1) 100 kg TPP  11 kg BDP  3 kg UV-1 1 kg Methyl acetate 440 kg Ethanol 110 kg

[0288] Preparation of Dope A9: Ordinary Temperature Dissolution

[0289] Raw materials described below were charged in a closed vessel,stirred at 30° C. for 20 min., followed by complete dissolution whilebeing heated and stirred.

[0290] A dope was allowed to stand to be cooled down to 30° C., andafter being subjected to a defoaming operation was filtered twice by useof Azumi Filter Paper No. 244 produced by Azumi Roshi Co., Ltd. toprepare dope A9. Cellulose ester (TAC6) 100 kg TPP  11 kg BDP  3 kg UV-1 1 kg Methyl acetate 440 kg Ethanol 110 kg

[0291] Using each TAC resin, each dope A1 to A12 was prepared byutilizing each additive, solvent and dissolution method described inTable 1.

[0292] Coating and Drying

[0293] Dope A1 described above was cast on a stainless steel supporthaving a surface temperature of 40° C. Being dried with a drying air of60° C., a film was peeled off from the support which was cooled at 10°C. at 60 seconds after casting. The peeled off film was stretched by atenter in the width direction (TD) and the longitudinal direction (MD)by 1.1 times and 1.05 times respectively, being dried at 100° C., widthclips were released at a residual solvent amount of 3%, drying wasfinished in a drying zone of 130° C. while further being transported bymany rolls, and the film was subjected to a knurling operation to give10 mm width and 8 μm height knuring on both edges of the film to preparecellulose ester film 1 having a thickness of 60 μm. The film width was1300 mm and the wounded length was 2,500 m.

[0294] Films 2 to 12 were prepared by using each dope in a similarmanner except that use of a tenter and time from casting to peeling offwere changed as described in Table 1. Herein, the item of a tenter inTable 1 shows that the preparation was performed by the foregoing methodwhen referred as “yes” and under free shrinkage without stretching whenreferred as “no”.

[0295] Each optical film 1 to 12 was obtained by providing prepared eachfilm with a metal oxide layer according to the following methodsdescribed below.

[0296] Formation of Metal Oxide (Tin Oxide) Layer

[0297] A metal oxide layer is formed on each cellulose ester film bymeans of atmospheric pressure plasma discharge treatment. Theatmospheric pressure plasma discharge treatment was performed by use ofan apparatus illustrated in FIG. 2. As a roll electrode, utilized is ajacket roll base material made of stainless steel, which has a coolingfunction by means of silicone oil circulation. Alumina is coveredthereon at a thickness of 1 mm by ceramic spattering, and after asolution of tetramethoxysilane diluted with ethyl acetate being coatedthereon and dried, it was subjected to a pore sealing treatment throughcuring by UV-irradiation to prepare a roll electrode provided with adielectric having a Rmax of 1 μm, which is connected to an earth(grounded).

[0298] On the other hand, as counter electrodes, a hollow stainlesssteel pipe is covered with a dielectric similar to the above in the sameconditions to be a group of electrodes which were standing opposite. Asan electric power source of a plasma discharge treatment apparatus,utilized was a high frequency power source produced by Nippon Denshi,and 4 W/cm2 of electric power, by adjusting a continuous frequencynumber to 13.56 MHz, was supplied. Herein, the roll electrode wasrotated by use of a drive being synchronized with transportation of acellulose ester film.

[0299] Herein, a metal oxide layer having a thickness of 0.1 μm wasformed by adjusting the electrode gap to 2 mm and the pressure of areactive gas to +1 kPa against atmospheric pressure. The reactive gascomposition utilized in a plasma discharge treatment is described below.

[0300] Reactive Gas for Preparation of Metal Oxide (Tin Oxide) LayerInert gas (helium) 99.4 volume %  Reactive gas (oxygen) 0.3 volume %Reactive gas (tetrabutyltin vapor) 0.3 volume %

[0301] Each film, after having been kept at 80° C. and 90% RH for threedays, was evaluated in respect with cracks generated in the surface of atin oxide layer and curl of each film.

[0302] Crack Evaluation

[0303] Cracks generated in a tin oxide layer which had been formed onthe surface of each cellulose ester film were observed visually andthrough an electron microscope. The evaluation ranks are as follows:

[0304] A: cracks were hardly observed, superior in transparency,

[0305] B: cracks were observed, however, no milky whitening,

[0306] C: cracks were observed and slight milky whitening,

[0307] D: marked cracks were generated and milky whitening.

[0308] Curl Evaluation

[0309] A sample sheet of 20 cm×20 cm was cut out from a film on which atin oxide layer had been formed, and, after being kept in a conditioningroom at a temperature of 25° C. and a humidity of 55% RH for 24 hours, arising distance of each four corner was measured while being placed on aflat board, to evaluate curl based on the maximum value thereof. Theevaluation ranks are as follows:

[0310] A: less than from 0 to 2 mm,

[0311] B: less than from 2 to 5 mm,

[0312] C: less than from 5 to 20 mm,

[0313] D: not less than 20 mm.

[0314] The results are shown in Table 2. TABLE 1 Cellu- Cellulose esterlos (100 kg each) Sol- Peeling ester Substi- Subst. Additive Dissolutionvent time Ten- Re- film Dope TAC tuent Degree Mw/Mn (kg) method (kg)(sec.) ter marks 1 A1 1 Acetyl 2.75 1.7 TPP (11), BDP (3), Cooled *1 60Yes Inv. UV-1 (1) 2 A2 1 Acetyl 2.75 1.7 E-1 (10), UV-2 (1) Cooled *1 60Yes Inv. 3 A3 1 Acetyl 2.75 1.7 EPEG (4), Cooled *1 60 Yes Inv. PDCH (6)UV-2 (1) 4 A4 2 Acetyl 2.75 2.2 E-1 (10), UV-2 (1) Cooled *1 60 Yes Inv.5 A5 3 Acetyl 2.60 2.5 TPP (11), BDP (3), Cooled *1 60 Yes Inv. UV-1 (1)6 A6 4 Acetyl 2.88 3.0 E-1 (10), UV-2 (1) Cooled *1 90 Yes Inv. 7 A7 5Acetyl 2.00 2.0 E-1 (10), UV-2 (1) Cooled *1 60 Yes Inv. Propi- 0.80onyl 8 A8 5 Acetyl 2.00 2.0 E-1 (10), UV-2 (1) Cooled *1 60 Yes Inv.Propi- 0.80 only 9 A9 6 Acetyl 1.90 2.5 TPP (11), BDP (3), Ordinary *160 Yes Inv. Propi- 0.70 UV-1 (1) temperature onyl 10 A10 3 Acetyl 2.602.5 TPP (11), BDP (3), Cooled *1 90 No Comp. UV-2 (1) 11 A11 7 Acetyl2.50 2.5 TPP (11), BDP (3), Cooled *1 90 Yes Comp. UV-2 (1) 12 A12 8Acetyl 2.75 4.0 TPP (11), BD P(3), Cooled *1 90 No Comp. UV-2 (1)

[0315] TPP: triphenyl phosphate

[0316] BDP: biphenyl diphenyl phosphate

[0317] EPEG: ethylphthalyl ethylglycolate

[0318] PDCH: dicyclohexyl phthalate

[0319] UV-1:5-chloro-2-(3,5-di-sec-butyl-2-hydroxyphenyl)-2H-benzotriazole

[0320] UV-2: 2-hydroxy-4-benzyloxy benzophenone

[0321] E-1: exemplary compound TABLE 2 Optical Cellulose Crack Curl filmester film evaluation evaluation Remarks 1 1 A B Invention 2 2 A AInvention 3 3 A A Invention 4 4 A A Invention 5 5 A B Invention 6 6 B BInvention 7 7 A A Invention 8 8 A A Invention 9 9 A A Invention 10 10 CC Comparison 11 11 C C Comparison 12 12 C C Comparison

[0322] A tin oxide layer was formed on each cellulose ester film toprovided an electric conductive layer. As a result, excellent resultshave been obtained; an optical film of the invention has minimal curland minimal crack generation.

Example 2

[0323] A hard coat layer was formed on each cellulose ester film (a filmbefore being provided with a tin oxide layer) prepared in Example 1 anda titanium oxide layer (a high refractive index layer) and a siliconoxide layer (a low refractive index layer) were formed thereon by aplasma treatment to prepare optical films 13 to 24 of the invention.

[0324] Preparation of a Hard Coat Layer Coating Solution and Formationof a Hard Coat Layer

[0325] MEK solution (solid concentration: 72%, silica content: 38%) of ahard coat material Desolite Z7503, manufactured by JSR Co., of 625 g wasdissolved in 375 g of a solvent mixture of methyl ethylketone/cyclohexanone=50/50 weight %. The mixture after having beenstirred, was filtrated through a polypropyrene filter having a porediameter of 0.4 μm to prepare a coating solution of a hard coat layer.

[0326] The foregoing coating solution for a hard coat layer was coatedon each cellulose ester film by use of a bar coater, and the coatedlayer, after having been dried at 90° C., was cured by UV irradiation toform a hard coat layer (refractive index: 1.49) having a thickness of 6μm.

[0327] Formation of a Titanium Oxide Layer (a High Refractive IndexLayer) and a Silicon Oxide Layer (a Low Refractive Index Layer) byPlasma Treatment

[0328] Utilizing the plasma discharge treatment apparatus which was usedin Example 1, the first titanium oxide layer (refractive index: 2.15,mean layer thickness: 15 nm), the first silicon oxide layer (refractiveindex: 1.46, mean layer thickness: 33 nm), the second titanium oxidelayer (refractive index: 2.15, mean layer thickness: 119 nm) and thesecond silicon oxide layer (refractive index: 1.46, mean layerthickness: 86 nm) were formed in this order on a UV cured resin layer ofeach cellulose ester film (1 to 12) having been provided with theforegoing UV cured resin layer (hard coat layer) to prepare opticalfilms 13 to 24 described in Table 3. As an electric power source for theplasma discharge treatment apparatus, utilized was a high frequencypower source, produced by Pearl Kogyo Co., and an electric power of6W/cm² was supplied to a discharge electrode with a continuous frequencynumber being adjusted to 2 MHz. A roll electrode was rotated by use of adrive being synchronized with transportation of a cellulose ester film.

[0329] Herein, the preparation was performed under an electrode gap of 2mm, and a pressure of a reactive gas of atmospheric pressure+1 kPa. Thecompositions of a reactive gas utilized for a plasma discharge treatmentwere shown below. Wherein, liquid components in a reactive gas weresupplied to an electric discharge portion as a vapor by use of avaporization device and being heated at 100° C.

[0330] Reactive Gas for Preparation of Titanium Oxide Layer (HighRefractive Index Layer) Inert gas (helium) 99.4 volume %  Reactive gas(oxygen) 0.3 volume % Reactive gas (tetraisopropoxy titanium vapor) 0.3volume %

[0331] Reactive Gas for Preparation of Silicon Oxide Layer (LowRefractive Index Layer) Inert gas (helium) 99.4 volume %  Reactive gas(oxygen) 0.3 volume % Reactive gas (tetraethoxy silane vapor) 0.3 volume%

[0332] Each optical film prepared was evaluated with respect to crackand curl in a similar manner to example 1. Further, measurement ofreflectance and evaluation of visibility of a liquid crystal panelcomprised of the optical film were performed.

[0333] Measurement of Reflectance

[0334] As a spectral reflectance of each sample, measured was a meanreflectance within a range of from 450 to 650 nm, by use of aspectrophotometer U-4000 type (produced by Hitachi Corp.) under acondition of 5 degree normal reflection. After the back-side surface ofthe observation side was subjected to a surface roughening treatmentfollowed by a light absorbing treatment by use of a black-colored sprayto prevent reflection of light at the back-side surface of a film,reflectance was measured.

[0335] Preparation of Liquid Crystal Panel and Evaluation of Visibility

[0336] Visibility was evaluated, by preparing a polarizing platecomprised of each optical film prepared above as shown below and bypasting up the plate on a liquid crystal display device.

[0337] Preparation of Polarizing Plate

[0338] (a) Preparation of Polarizing Film

[0339] A polyvinyl alcohol film having a thickness of 120 μm wasuni-axially stretched (at a temperature of 110° C. and a stretchingmagnification of 5 times). This was immersed in a aqueous solutioncomprising a ratio of 0.075 g of iodine, 5 g of potassium iodide and 100g of water for 60 seconds, and then in a aqueous solution comprising aratio of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of waterbeing kept at 68° C. This was washed with water and dried to obtain along roll of polarizing film.

[0340] (b) Preparation of Polarizing Plate

[0341] Next, polarizing plate was prepared by pasting up a polarizingfilm and each protective film of a polarizing plate each other accordingto the following processes 1 to 5. Process 1: Each optical film preparedin Example 2 was immersed in 2 mol/L sodium hydroxide solution at 60° C.for 90 seconds, followed by being washed with water and dried. Thesurface provided with a metal oxide layer was protected from alkali bypasting up a delaminatable protective film (PET) in advance.

[0342] Each cellulose ester film prepared in Example 1 (without a metaloxide layer) was immersed in 2 mol/L sodium hydroxide solution at 60° C.for 90 seconds, followed by being washed with water and dried.

[0343] Process 2: The polarizing films described above were immersed ina polyvinyl alcohol adhesive bath having a solid content of 2 weight %for 1 to 2 seconds.

[0344] Process 3: An excess adhesive having been adhered on a polarizingfilm in Process 2 was removed by slight wiping, and the film wasarranged to make an accumulation by being sandwiched with a celluloseester film which had been alkali treated in Process 1 and an opticalfilm comprised of the same cellulose ester film.

[0345] Process 4: Pasting up was performed by use of two rotating rollsat a pressure of from 20 to 30 N/cm² and a speed of approximately 2m/min. In this occasion, the process was performed with caution not toincorporate bubbles.

[0346] Process 5: Each polarizing plate was prepared by drying thesamples prepared in Process 4 in a drier at 80° C. for 3 minutes.

[0347] Evaluation as a Liquid Crystal Display Device

[0348] A liquid crystal display device was prepared by peeling apolarizing plate off carefully from the observing side of a liquidcrystal display panel available on the market (Color liquid crystaldisplay MultiSync LCD 1525J: Type LA-1529HM, produced by NEC) andpasting up the polarizing plate prepared above while placing the metaloxide layer outside and aligning a polarizing direction.

[0349] Each crystal display panel prepared above was evaluated asfollows.

[0350] Visibility Evaluation

[0351] Crystal liquid displays were evaluated visually.

[0352] A: black is tight and distinct to yield good contrast, and nocolor shading of reflective light is observed,

[0353] B: black is tight and distinct to yield good contrast, however,slight color shading of reflective light is observed,

[0354] C: black is loose and somewhat inferior in distinction to yieldinferior contrast, and color shading of reflective light is observed,

[0355] D: black is loose and inferior in distinction to yield inferiorcontrast, and color shading of reflective light is significant.

[0356] Evaluation results are shown in Table 3. TABLE 3 CelluloseReflec- Optical ester tance Visi- film film Crack Curl (%) bilityRemarks 13 1 B B 0.3 B Invention 14 2 A A 0.3 A Invention 15 3 A A 0.3 AInvention 16 4 A A 0.3 A Invention 17 5 B B 0.3 B Invention 18 6 B B 0.3B Invention 19 7 A A 0.3 A Invention 20 8 A A 0.3 A Invention 21 9 A B0.3 A Invention 22 10 C C 0.4 C Comparison 23 11 C C 0.4 C Comparison 2412 C C 0.4 C Comparison

[0357] Samples of the invention showed minimal curl and few cracks, aswell as a low reflectance of the surface, and have been proved toexhibit superior visibility when they comprise a liquid crystal displaydevice.

Example 3

[0358] A metal oxide layer (containing titanium oxide) was formed bycoating on the cellulose ester films prepared in Example 2 provided witha hard coat layer.

[0359] Preparation of a Medium Refractive Index Layer/a High RefractiveIndex Layer/a Low Refractive Index Layer

[0360] Preparation of Titanium Dioxide Dispersion

[0361] Titanium oxide (primary particle weight average diameter: 50 nm,refractive index: 2.70) of 30 weight parts, 4.5 weight parts of ananionic diacrylate monomer (PM21, manufactured by Nippon Kayaku Co.,Ltd.), 0.3 weight parts of a cationic methacrylate monomer (DMAEA,manufactured by Kojin Co., Ltd.) and 65.2 weight parts of methyl ethylketone were dispersed by a sand grinder to prepare a titanium dioxidedispersion.

[0362] Preparation of a Coating Solution for a Medium Refractive IndexLayer

[0363] A photopolymerization initiator (Irgacure 907, manufactured byCiba Geigy Co.) of 0.14 g and a photosensitizer (Kayacure DETX,manufactured by Nippon Kayaku Co., Ltd.) of 0.04 g were dissolved in151.9 g of cyclohexanone and 37.0 g of methyl ethyl ketone. Further,after 6.1 g of the foregoing titanium dioxide dispersion and 2.4 g of amixture of dipentaerythritol pentaacrylate and dipentaerythritolhexaacrylate (DPHA, manufactured by Nippon Kayaku Co., Ltd.) being addedand stirred at room temperature for 30 minutes, the solution wasfiltered through a polypropyrene filter having a pore size of 0.4 μm toprepare a coating solution for a medium refractive index layer. Thecoating solution was coated and dried on a cellulose ester film, andafter being cured by UV ray, refractive index was measured to obtain amedium refractive index layer having a refractive index of 1.72.

[0364] Preparation of a Coating Solution for a High Refractive IndexLayer

[0365] A photopolymerization initiator (Irgacure 907, manufactured byCiba Geigy Co.) of 0.06 g and a photosensitizer (Kayacure DETX,manufactured by Nippon Kayaku Co., Ltd.) of 0.02 g were dissolved in1152.8 g of cyclohexanone and 37.2 g of methyl ethyl ketone. Further,after the foregoing titanium dioxide dispersion and the mixture ofdipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate(DPHA, manufactured by Nippon Kayaku Co., Ltd.) being added, whileincreasing titanium dioxide ratio so as to adjust the refractive indexto match a high index refractive index layer, and the system beingstirred at room temperature for 30 minutes, the solution was filteredthrough a polypropyrene filter having a pore size of 0.4 μm to prepare acoating solution for a high refractive index layer. The coating solutionwas coated and dried on a cellulose ester film, and after being cured byUV ray, refractive index was measured to obtain a high refractive indexlayer having a refractive index of 1.95.

[0366] Preparation of a Coating Solution for a Low Refractive IndexLayer

[0367] Silane coupling agent (KBM-503, manufactured by Shinetsu SiliconeCo., Ltd.) of 3 g and 0.1 M/L hydrochloric acid of 2 g were added to 200g of a methanol dispersion solution of silica fine particles having amean particle diameter of 15 nm (Methanol silica sol, manufactured byNissan Kagaku Co., Ltd.) and after being stirred at room temperature for5 hours, the system was kept standing for three days to obtain adispersion of silica fine particles having been subjected to silanecoupling treatment. Isopropyl alcohol of 58.35 g and diacetone alcoholof 39.34 g were added to 35.04 g of the dispersion. Further, a solution,in which 102 g of a photopolymerization initiator (Irgacure 907,manufactured by Ciba Geigy Co.) and 0.51 g of a photosensitizer(Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) were dissolvedin 772.85 g of isopropyl alcohol, was added to the system, and 25.6 g ofa mixture of dipentaerythritol pentacrylate and dipentaerythritolhexacrylate (DPHA, manufactured by Nippon Kayaku Co., Ltd.) was addedand dissolved. The solution obtained of 67.23 g was added to a mixtureof the foregoing dispersion, isopropyl alcohol and diacetone alcohol.The mixture was stirred at room temperature for 20 minutes and filteredthrough a polypropyrene filter having a pore size of 0.4 μm to prepare acoating solution for a low refractive index layer. The coating solutionwas coated and dried on a cellulose ester film, and after being cured byUV ray, a refractive index was measured to be 1.45.

[0368] Preparation of Anti-Reflection Film

[0369] The foregoing coating solution for a medium refractive indexlayer was coated by utilizing a bar coater, on the cellulose ester filmsprepared in Example 2 provided with a hard coat layer, and after beingdried at 60° C., the coated layer was cured by irradiating UV ray toform a medium refractive index layer (refractive index: 1.72). Theforegoing coating solution for a high refractive index layer was coatedthereon by utilizing a bar coater, and after being dried at 60° C., thecoated layer was cured by irradiating UV ray to form a high refractiveindex layer (refractive index: 1.95). The foregoing coating solution fora low refractive index layer was coated further thereon by utilizing abar coater, and after being dried at 60° C., the coated layer was curedby irradiating UV ray to form a low refractive index layer (refractiveindex: 1.45).

[0370] For each sample obtained, evaluations with respect to crack, aswell as visibility of a liquid crystal display panel composed of thesample and further the following evaluation on unevenness of a layerthickness were performed.

[0371] Evaluation on Unevenness of Layer Thickness

[0372] Unevenness of layer thickness, that is coating unevenness, ofeach optical film was evaluated according to the following criteria.

[0373] A mean layer thickness of a metal oxide layer formed on thesurface of a cellulose ester film was determined by preparing a sectionof an accumulation and observing the section through a transmissionelectron microscope (hereinafter referred as TEM).

[0374] A section was prepared by burying an accumulation together with abase material in an epoxy burying resin for pretreatment of electronmicroscopy observation, and the surface of the accumulation beingfocusing scanned with Ga ion beam by use of a focused ion beam (FIB) tocut out a section of a thin slice having a thickness of approximately100 nm.

[0375] In observation through TEM, it was performed at a magnificationof from 50,000 to 500,000 times and images in bright ground wereobserved and recorded. Unevenness of layer thickness (coatingunevenness) was determined as a difference (nm) between the maximum andthe minimum of the layer thickness based on values obtained at arbitrary25 points in a area of 5 cm×5 cm. Evaluation ranks are as follows:

[0376] A: less than 1 nm,

[0377] B: less than from 1 to 4 nm,

[0378] C: less than from 4 to 10 nm,

[0379] D: not less than 10 nm.

[0380] The evaluation results are shown in Table 4. In the table theyare expressed as coating unevenness. TABLE 4 Cellulose Optical esterCoating Visi- film film Crack unevenness bility Remarks 25 1 B B BInvention 26 2 A A A Invention 27 3 A A A Invention 28 4 A A A Invention29 5 B B B Invention 30 6 B B A Invention 31 7 A A A Invention 32 8 A AA Invention 33 9 A B B Invention 34 10 C C C Comparison 35 11 C C CComparison 36 12 C C C Comparison

[0381] It is clear that samples of the invention have minimal crack aswell as minimal unevenness of layer thickness and are superior invisibility as a liquid crystal display device comprising the samples.

[0382] By utilizing a cellulose ester film of the invention, an opticalfilm, having minimal crack as well as minimal coating unevenness, smallcurl of the film and excellent visibility is obtained.

What is claimed is:
 1. An optical film obtained by a process comprisingthe steps of: (a) casting a dope comprising a cellulose ester and anon-chlorinated solvent on a metal support, the cellulose ester having atotal acyl substitution degree of 2.6 to 2.85 and having a ratio of aweight-average molecular weight to a number-average molecular weight of1:1 to 3:1; (b) drying the cast dope on the metal support so as toobtain a cellulose ester film; (c) pealing the cellulose ester film fromthe metal support; (d) further drying the cellulose ester film whileproviding a longitudinal stretch or a lateral stretch to the celluloseester film; and (e) providing a metal oxide layer on the cellulose esterfilm.
 2. The optical film of claim 1, wherein the process furthercomprises the step of: (f) providing an interlayer between the cellulosefilm and the metal oxide layer.
 3. The optical film of claim 1, whereinthe dope is prepared with a cold dissolving method.
 4. The optical filmof claim 1, wherein the dope further comprises an additive in an amountof 0.5 to 30 weight % based on the total weight of the dope, theadditive being a compound having at least three substituents selectedfrom the group consisting of a phenyl group, a cycloalkyl group and acycloalkenyl group.
 5. The optical film of claim 1, wherein the metaloxide layer is provided using a plasma CVD method.
 6. The optical filmof claim 1, wherein the metal oxide layer comprises metal oxideparticles.
 7. A polarization plate comprising the optical film ofclaim
 1. 8. A display apparatus comprising the optical film of claim 1.9. A process for producing an optical film comprising the steps of: (a)casting a dope comprising a cellulose ester and a non-chlorinatedsolvent on a metal support, the cellulose ester having a total acylsubstitution degree of 2.6 to 2.85 and having a ratio of aweight-average molecular weight to a number-average molecular weight of1:1 to 3:1; (b) drying the cast dope on the metal support so as toobtain a cellulose ester film; (c) pealing the cellulose ester film fromthe metal support; (d) further drying the cellulose ester film whileproviding a longitudinal stretch or a lateral stretch to the celluloseester film; and (e) providing a metal oxide layer on the cellulose esterfilm.
 10. The process of claim 9, further comprising the step of: (f)providing an interlayer between the cellulose film and the metal oxidelayer.
 11. The process of claim 9, wherein the step of pealing thecellulose ester film from the metal support is finished within 60seconds after drying the cast dope on the metal support.
 12. The processof claim 9, wherein the step of pealing the cellulose ester film fromthe metal support is finished with 60 second after drying the cast dopeon the metal support, and the process further comprising the step of:(f) providing an interlayer between the cellulose film and the metaloxide layer.